KABUL, Afghanistan >> The Afghan Taliban are showing signs of increasing strain after a number of killings, arrests and internal disputes that have affected them even in their Pakistan haven, Afghan security officials and Afghans with contacts in the Taliban say.

The killings, coming just as the insurgents are mobilizing for the new fighting season in Afghanistan, have unnerved many in the Taliban and have spread a climate of paranoia and distrust within the insurgent movement, the Afghans said.

Three powerful Taliban commanders were killed in February in the southwestern Pakistani city of Quetta, well known to be the command center of the Taliban leadership, according to an Afghan businessman and a mujahedeen commander from the region with links to the Taliban. A fourth commander, a former Taliban minister, was wounded in the border town of Chaman in March, in a widely reported shooting.

There have also been several arrests in Pakistan of senior Taliban commanders, including those from Zabul and Kabul provinces and the shadow governor of Herat, Afghan officials said. Mullah Agha Muhammad, a brother of Mullah Baradar, the former Taliban second in command who was arrested by Pakistan security forces over a year ago to stop him from negotiating with the Afghan government, was also detained briefly to send out the same warning, said the chief of the Afghan border police in Kandahar, Col. Abdul Razziq.

While the arrests have been conducted by Pakistan security forces, no one seems to know for sure who is behind the killings. Members of the Taliban attribute them to U.S. spies, running Pakistani and Afghan agents, in an extension of the U.S. campaigns that have used night raids to track down and kill scores of midlevel Taliban commanders in Afghanistan and drone strikes to kill militants with links to al-Qaida in Pakistan’s tribal areas.

Others, including Pakistani and Afghan Parliament members from the region, say that the Pakistani intelligence agencies have long used threats, arrests and killings to control the Taliban and that they could be doing so again to maintain their influence over the insurgents.

Afghan officials in Kabul denied any involvement in attacks on the Taliban inside Pakistan, as did U.S. and NATO military officials. “We’ve heard of infighting that reportedly has led to internal violence at several points in recent months,” one senior U.S. military official said of the Taliban, asking not to be named because of the sensitivity of discussing events in Pakistan. Military forces were not involved, he added.

Whatever the case, Taliban commanders and fighters, who used to be a common sight in parts of Quetta, have now gone underground and are not moving around openly as before. Two members of the Taliban, including a senior official, declined to talk about the issue of killings on the telephone, saying it was too dangerous. Many will not answer their phones at all.

The Taliban have been under stress since U.S. forces doubled their presence in southern Afghanistan last year and greatly increased the number of special forces raids targeting Taliban commanders. Yet they still control a number of remote districts and in those areas the insurgents can still muster forces to storm government positions, as demonstrated by their capture of a district in Afghanistan’s eastern Nuristan province this week.

While there is still some debate over the insurgents’ overall strength, Pakistanis with deep knowledge of the Afghan Taliban say that they have suffered heavy losses in the last year and that they are struggling in some areas to continue the fight.

“The Afghan Taliban have, I think, run into problems,” said Rustam Shah Mohmand, a former Pakistani interior minister who served as ambassador in Afghanistan after 2001 and as a peace negotiator with the Taliban. “So many of them have been killed in the last one to one-and-a-half years as a consequence of targeted assassinations,” he said in an interview. “That has depleted the strength, capacity and ability of the Taliban.”

Commanders were without communications and resources and were struggling to find recruits to replace those killed, he said.

One Taliban commander from Kunar province said losses had been so high that he was considering going over to the side of the Afghan government in order to get assistance for his beleaguered community. “This does not mean the Taliban will stop fighting, but maybe it will be at a reduced level,” Mohmand said. Insurgents have already switched tactics to suicide attacks on soft targets — such as recent attacks on a bank, an army recruitment center and a construction company that all caused high casualties — because they are not capable of confronting U.S. and NATO forces in conventional battles, said Samina Ahmed, director of the International Crisis Group in Pakistan.

The Taliban have always been able to survive temporary setbacks on the battlefield by pulling back to Pakistan, where many have homes and businesses. Fighters have also found sanctuary and medical care in the anonymity of the refugee camps where over a million Afghans have lived for a generation through Afghanistan’s various wars, and in the outlying suburbs of Pakistani cities like Peshawar, Quetta and Karachi.

Yet Pakistan has become a much more uncertain environment for the Taliban as the new civilian government is openly hostile to them, the military seeks to control them and influence any future settlement they make with Kabul, and the United States increases its attacks in Pakistan, two former ambassadors, Lakhdar Brahimi and Thomas Pickering, who lead an International Task Force on Afghanistan, reported last week.

In the anti-U.S. spy mania that seized Pakistan after an American working for the CIA, Raymond A. Davis, shot and killed two Pakistanis in the city of Lahore on Jan. 27, Pakistani officials and politicians have accused the CIA of running numerous covert programs around the country.

A Pakistani intelligence official confirmed that CIA operatives were using their own local agents to target al-Qaida-linked militants with drones in Pakistan’s tribal areas. That official speculated that they could be trying to expand that campaign to reach other Pakistani militants and Afghan Taliban inside Pakistan.

The CIA has been formulating such a plan for months, according to two former Afghan security officials who spoke on condition of anonymity because of the covert nature of their work. The Americans have been using tribesmen, including members of the Taliban they have turned, to attack other Taliban groups in the border areas, one of the officials said.

But others, including officials on both sides of the border, said it could be the work of Pakistan’s premier spy agency, the Directorate for Inter-Services Intelligence, or ISI.

“Their method is brutality,” Abdul Rahim Mandokhail, a Pakistani senator from the southwestern border region near Quetta, said of the ISI. “If there is only a little opposition, their method is to kill the man,” he said. He had no specific information on recent killings, because it was too dangerous to investigate such things, he said.

A Pakistani government official working in the border region said both U.S. and Pakistani intelligence agencies favored different insurgent groups and were striking at each other’s.

The three commanders killed in Quetta last month all led units fighting in Marjah, in Helmand, the southern Afghan province where U.S. Marines have struggled to establish security after more than a year of counterinsurgency operations.

One of the commanders was Hajji Khalil, in his late 30s, who commanded several groups of fighters in Marjah, according to Baz Gul Khan, a pro-government militia leader in Marjah. “He was famous in all of Marjah,” Khan said. “He had about 300 men or more.”

Hajji Khalil was killed in his own house, by two men who appeared to be Taliban who stayed the night with him in his guest room. The two men left unseen by the street entrance, and the next morning Hajji Khalil’s family found him slain in the room, an Afghan businessman who is close to the Taliban said. He did not want to be named for fear of his safety.

Another commander, known as Mansour, was gunned down while riding his motorbike along Saryab Road west of the city. He led up to five units of men in Marjah and operated out of a rented house in Quetta, a clear sign that he enjoyed the patronage of the ISI, the businessman said.

He did not know the name of the third Taliban commander who was killed but said that he was also from Marjah and that he was responsible for communication between the senior Taliban and the fighters.

A fourth commander, Manzoor Ahmed, the former Taliban sports minister, was shot four times by unidentified assailants on the way to his office in the border town of Chaman on March 3, the official Pakistani news agency, The Associated Press of Pakistan, reported. Still, he survived.

The militia leader, Khan, said the killings were a sign that the Taliban was in decline. “We have a saying, that when a goat becomes sick, he attracts every disease,” he said. “I think the Taliban have lost momentum, they are losing the fight and so the Pakistanis do not need them and so they will kill them,” he said.

U.S., NATO and Afghan officials said Taliban leaders are struggling to adapt to the pressures on the movement after heavy losses on the battlefield last year and are finding commanders reluctant to return to Afghanistan to fight.

“Almost 900 were killed last year,” a senior Afghan security official said. “And now the commanders are telling their leaders: ‘You have a nice life, your kids are in school, you are going on trips to Dubai, and you are telling us to go and fight?”’