The Local Coordination Committees, a group opposed to the regime of President Bashar Assad, said Syrian air force MiG fighters carried out the attack on Maarat al-Noaman in Idlib Province, The New York Times reported.
Videos posted online showed scenes of the destruction, including rescue workers and others searching devastated apartment buildings for signs of victims, the Times said.
The development came as activist groups said at least 28,000 Syrians have been "forcibly disappeared" by regime forces during the 19-month conflict with opposition groups. The international activist group Avaaz says the kidnappings are part of the Syrian government's strategy to silence dissent, CNN reported Thursday.
Avaaz campaign director Alice Jay said in a statement Syrians "are being plucked off the street by Syrian security forces and paramilitaries and being disappeared into torture cells. This is a deliberate strategy to terrorize families and communities -- the panic of not knowing whether your husband or child is alive breeds such fear that it silences dissent."
Jay said her human rights group based its allegations on information provided by other human rights groups.
One of those groups, the Syrian Network for Human Rights, says it has the names of 18,000 people who are missing. Fadel Adbul Ghany, an attorney for SNHR, said the group has information about 10,000 other cases, but families are too scared to give the group names.
Such information cannot be independently confirmed because Syria does not allow international news organizations to enter the country.
News about the disappearances came as leaders in Iran and Turkey voiced support for a cease-fire proposal offered by new U.N.-Arab League envoy to Syria Lakdar Brahimi.
Syrian leaders, however, said they were skeptical the rebels would honor the temporary cease-fire during the three-day Muslim holiday of Eid al-Adha, which begins Oct. 26, the Times reported Thursday.
Brahimi has spent the last several days consulting with Middle East leaders, discussing possible ways to end the civil unrest that began in March 2011.
Both Turkey, which backs the rebels and has called for Assad to step down, and Iran, which backs Assad's regime, publicly endorsed Brahimi's effort Wednesday, the Times said. Turkey is home to more than 100,000 Syrian refugees.
Iranian President Mahmoud Ahmadinejad, who met this week with Turkish Prime Minister Recep Tayyip Erdogan during a regional summit in Baku, Azerbaijan, was quoted by Iran's state-run media as saying he supported the Syria truce proposal saying, "any group that derives power through war and means to continue war has no future."
Turkish Foreign Minister Ahmet Davutoglu was quoted by Turkey's Anatolian News Agency as saying a cease-fire was desirable but a longer-term truce would require "certain measures for its sustainability."
Brahimi urged the Syrian government to support the cease-fire, saying he had guarantees from rebel leaders that they would observe the cease-fire if the government acted first, the Times said. However, a government-backed newspaper expressed doubt insurgents, who lack a unified command, would or could uphold a cease-fire.
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