BEIRUT (AP) — Syrian warplanes struck a strategic rebel-held town in the country’s north in an attempt to reopen a key supply route Tuesday, three days before the U.N.-proposed start of a truce that appears increasingly unlikely to take hold.

The U.N.-Arab League envoy to Syria, Lakhdar Brahimi, has suggested that both sides in Syria’s 19-month-old conflict lay down their arms during Eid al-Adha, a four-day Muslim holiday that begins Friday. However, neither Syrian President Bashar Assad nor rebels fighting to topple him have committed to a truce, and Brahimi has not explained in public how such a truce would be monitored.

Activists reported clashes between regime forces and rebels in several areas of Syria on Tuesday.

One of the heaviest battles raged in Maaret al-Numan, a town that straddles the main highway between Aleppo, Syria’s largest city and commercial hub, and the capital Damascus.

Opposition fighters seized the town earlier this month, and their presence there has hampered the regime’s ability to send supplies and reinforcements to northwestern Syria, including Aleppo, where government troops are bogged down in a bloody fight for control of the city.

On Tuesday, Syrian warplanes attacked Maaret al-Numan and the village of Mar Shamsheh, as troops and rebels battled over a nearby Syrian military camp that has been under siege for days, according to the Britain-based Syrian Observatory for Human Rights, an activist group.

Amateur video posted Monday showed rebel fighters unleashing heavy bursts of machine-gun fire toward a convoy heading to the besieged army camp. Syria restricts access to foreign reporters and the authenticity of the video could not be independently confirmed.

The Syrian uprising erupted in March 2011 as a popular uprising against the Assad regime and has since escalated into a full-blown civil war.

More than 34,000 people have been killed in the past 19 months, said Rami Abdul-Rahman, the head of the Observatory, which relies on a network of activists on the ground. This figure includes civilians and rebel fighters, but also more than 8,000 regime soldiers, he said.

Abdul-Rahman said there were no signs on the ground that rebels or government troops were preparing to halt fighting during Eid al-Adha, or the Feast of Sacrifice. “Until we see evidence on the ground, it means it’s a dream only,” he said of the proposed truce.

The head of the Syrian National Council, the main Syrian opposition group in exile, said chances for a cease-fire are slim.

SNC chief Abdelbaset Sieda told The Associated Press on Tuesday that rebel fighters are willing to halt fighting during the holiday, but will respond if attacked. He said he doubts the regime will honor the cease-fire and that Brahimi’s plan is too vague.

“Brahimi hasn’t any mechanism to observe the situation,” Sieda said by phone from Stockholm, Sweden. “Now he is saying every side can do that (halt fighting) by itself.”

In Damascus, Syria’s deputy foreign minister, Faisal Mekdad, said the Assad regime is cooperating with Brahimi. “We are always optimistic,” he said when asked about the chances of a cease-fire.

However, Brahimi said after a visit to Damascus on Sunday that he did not get a commitment to the truce from the regime.

The relentless fighting in Syria has forced hundreds of thousands of people to flee the country to escape the violence.

The U.N. refugee agency said Tuesday that Lebanon has become the third Syrian neighbor to host more than 100,000 refugees from Syria’s civil war.

At least 101,283 people have registered as refugees in Lebanon, said agency spokeswoman Melissa Fleming. This compares to more than 105,000 in Jordan, at least 101,000 in Turkey, more than 42,000 in Iraq and 6,800 in North Africa.

Governments bordering Syria estimate tens of thousands more Syrian refugees have not yet registered, including an estimated 70,000 in Turkey who live outside refugee camps, she said.

Jordan alone says it hosting some 210,000 Syrian refugees, which Amman says has strained the country’s health care, water and electricity sectors.

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Associated Press writers Bassem Mroue in Beirut, Albert Aji in Damascus, Syria, and John Heilprin in Geneva contributed to this report.