BEIRUT >> Gunfire reverberated Tuesday in the southern Syrian city of Daraa where the dead still lay unclaimed in the streets a day after a brutal government crackdown on the popular revolt against President Bashar Assad, residents said.

A Syrian human rights group said authorities detained dozens across the country, mainly in several Damascus suburbs and in the northern coastal city of Jableh.

The Syrian army, backed by tanks and snipers, launched a deadly raid before dawn Monday on Daraa, where the uprising in Syria started more than a month ago. At least 11 people were killed in the southern city.

A relentless crackdown since mid-March has killed more than 400 people across Syria, with 120 dead over the weekend, rights groups said. That has only emboldened protesters who started their revolt — inspired by uprisings in the Arab world — with calls for modest reforms but are now increasingly demanding Assad’s downfall.

The White House has stepped up its condemnation of Assad’s regime, but stopped well short of demanding his ouster. U.S. officials said Washington has begun drawing up targeted sanctions against him, his family and his inner circle to boost pressure on them to halt the repression.

Washington was conferring with European countries and the United Nations about options.

British Foreign Secretary William Hague said Britain also was working with other members of the U.N. Security Council "to send a strong signal to the Syrian authorities that the eyes of the international community are on Syria." The U.N. will discuss Syria later Tuesday.

The United States told all its nonessential staff and the families of all its embassy workers to leave the country, but kept the facility open for limited services. It also advised all Americans to defer travel to Syria and advised those already in the country to leave. On Sunday, Britain urged its citizens to leave Syria.

Turkish Prime Minister Recep Tayyip Erdogan called Assad and urged him to show "restraint." Turkey’s ambassador met Syrian Prime Minister Adel Safar to express "deep concern and sorrow" over the many lives lost, the prime minister’s office and the Turkish media reported.

The head of the Syrian Observatory for Human Rights, Rami Abdul-Rahman, who provided the death toll of more than 400 people since the uprising began last month, said that figure did not include those killed in the raids on Daraa and Douma, a Damascus suburb. It also did not include the number of Syrian troops killed, he added..

Abdul-Rahman couldn’t provide a precise figure for those arrested Tuesday because it was difficult to get through to Daraa after authorities cut telephone service in the city.

A Daraa resident told The Associated Press on Tuesday "dead bodies were still in the streets because no one has been able to remove them."

"We are being subjected to a massacre," the man screamed over the telephone as gunfire crackled in the background. "Children are being killed. We have been without electricity for three days. We have no water."

The man said Syrian special forces were in the streets of the impoverished city near the border with Jordan. Tanks had opened fire in the city, he added.

The witness, contacted via a Jordanian cellphone, spoke on condition of anonymity for fear of reprisal, as did other witnesses and residents contacted across Syria.

Syria has banned nearly all foreign media and restricted access to trouble spots since the uprising began, making it almost impossible to verify the dramatic events shaking one of the most authoritarian, anti-Western regimes in the Arab world.

In Douma, which saw an intense raid Monday, a resident said authorities closed the private Hamdan Hospital after ordering all families of patients there to take them home. No reason was given for the closure and three doctors who worked there have been detained, the resident said.

The streets of Douma were almost empty Tuesday, with schools and most shops closed. There was an intense security presence, with agents at checkpoints asking people for their identity cards.

Garbage was piling up in Douma because sanitation crews have not worked for days due to the violence.

In the central city of Homs, life was almost back to normal — except for intense security, a witness said. A few hundred people demonstrated in Homs on Monday in support of Daraa, the witness said

Daraa, located in a parched region of 300,000 people in the south, has seen some of the worst bloodshed in the past five weeks as the uprising gained momentum. Recently, the city has absorbed many rural migrants who can no longer farm after years of drought.

The uprising was touched off by the arrest of teenagers who scrawled anti-government graffiti on a wall.

Last week, Assad fulfilled a key demand of protesters by abolishing nearly 50-year-old emergency laws that had given the regime a free hand to arrest people without cause. But he coupled the concession with a stern warning that protesters would no longer have an excuse to hold mass protests, and any further unrest would be considered "sabotage."

When protesters defied his order and held demonstrations Friday — the main day for protests around the Arab world — they were met with a gunfire, tear gas and stun guns.

The attack on Daraa was by far the biggest in scope and firepower. Video purportedly shot by activists showed tanks rolling through streets and grassy fields with soldiers on foot jogging behind them.

State-run television quoted a military source as saying army units entered the city to bring security "answering the pleas for help by residents of Daraa."

Syria has a pivotal role in most of the flashpoint issues of the Middle East — from the Arab-Israeli peace process to Iran’s widening influence. Instability has thrown into disarray the U.S. push for engagement with Damascus, part of Washington’s hopes to peel the country away from Hamas, Hezbollah and Tehran.