Car bombs, shelling and airstrikes have become common in the civil war, which has killed more than 100,000 people and driven another 7 million around a third of the country's pre-war population from their homes since March 2011. The conflict has heavily damaged cities and Syria's social fabric as it has taken on increasingly dark sectarian overtones, pitting a primarily Sunni Muslim rebel movement against a regime dominated by President Bashar Assad's Alawite sect an offshoot of Shiite Islam.
Amateur video posted online showed civilians and men with guns sorting through the smoldering wreckage of the bombing. Smoke still hung over the blast site, while a portion of the mosque's roof had collapsed. The video's narrator accused Assad's regime of carrying out the bombing and used a pejorative term for Shiites.
The video appeared genuine and corresponds to other Associated Press reporting of the events depicted.
The Syrian state news agency accused the opposition of being behind the blast, saying "terrorists" detonated the bomb after a disagreement over divvying up weapons and ammunition. The government calls those trying to overthrow it "terrorists."
The fighting has shown no sign of abating and could complicate the mission of U.N. chemical weapons investigators who are back in Syria this week.
The U.N. office in Damascus said the team, which returned Wednesday, will visit seven sites that have been found to "warrant investigation" and are continuing to work "on a comprehensive report that it hopes will be ready by late October."
The team initially visited Syria last month to investigate three alleged chemical attacks this year. But just days into the visit, the rebel-held Damascus suburb of Ghouta was hit by a chemical attack, and the inspectors turned their attention to that case. The inquiry determined that the nerve agent sarin was used in the Aug. 21 attack, but it did not assess who was behind it.
Among the new sites the team plans to investigate is the northern town of Khan al-Assal, outside the city of Aleppo. Assad's government and Syrian rebels have traded accusations of chemical weapons use in a March 19 attack.
The team also plans to look into allegations of chemical agents being used in the Damascus neighborhood of Jobar, the northern town of Saraqeb, the Sheik Maksoud neighborhood of Aleppo and three other sites.
The visit coincides with a sharp uptick in fighting in northern Syria between al-Qaida's Islamic State in Iraq and the Levant and more moderate rebel factions associated with the Free Syrian Army, the loose-knit collection of rebel brigades backed by the U.S. and its allies.
The infighting, which saw ISIL expel more mainstream rebels from areas near the Turkish border last week, has threatened to further divide opposition forces already outgunned by Assad's troops.
The Observatory said ISIL has given the FSA-affiliated Northern Storm Brigade until Saturday evening to hand over their weapons and "repent." In turn, the Northern Storm Brigade accused ISIL fighters of abandoning the fight against Assad, and promised "an all-out war in Aleppo and its suburbs" against the al-Qaida-linked fighters.
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Associated Press writer Albert Aji in Damascus, Syria, contributed to this report.
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