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Associated Press
In this Saturday, Oct. 20, 2012 file photo, a Free Syrian Army fighter shoots his machine gun towards Syrian Army positions in the Amriya district of Aleppo, Syria. Piece by piece, Syria's rebels are slowly starting to expand their arsenal and get their hands on more advanced weapons, something that has been their constant aim in the 19-month-old uprising against the regime of President Bashar Assad. The process still appears to be haphazard and improvised: Far from a reliable, organized pipeline, it often remains a scramble by individual units in the highly fragmented rebel forces to obtain what they can. Most units still rely on their staple arsenal of automatic weapons, hand grenades and rocket-propelled grenades. (AP Photo/ Manu Brabo, File)

BEIRUT — Syrian warplanes on Tuesday struck a strategic rebel-held town in the country's north in an attempt to reopen a key supply route, activists said, as a U.N.-proposed cease-fire meant to start this week appeared increasingly unlikely to take hold.

The U.N.-Arab League envoy to Syria 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 international envoy Lakhdar Brahimi has not said how such a truce would be monitored.

Syria's stalemated civil war, which has frequently spilled over Syria's borders and threatens to destabilize an already volatile region, featured prominently in the final pre-election debate Monday in the U.S. between President Barack Obama and his Republican challenger, Mitt Romney,

Both men said they would not send American troops to Syria, but Romney pledged to help arm rebels after vetting the intended recipients, earning him praise from Syrian opposition leaders. Obama warned of the risk of giving the rebels heavy weapons that could fall into the wrong hands and later be used against the U.S. or its allies.

"By not arming the (rebel) Free Syrian Army with heavy weapons, he (Obama) is giving Assad the upper hand," said Muhieddine Lathkani, a member of the Syrian National Council, an umbrella of opposition groups.

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The rebels have said they need heavier weapons to counter Assad's military superiority, particular from the air. Since the summer, the regime has increasingly pounded rebel positions with warplanes and helicopter gunships.

On Tuesday, government aircraft 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. The activist group reported more than two dozen casualties among the rebels, but did not have the breakdown of killed and wounded.