BEIRUT, Lebanon — A force of Syrian Army defectors claimed responsibility for a Wednesday attack that killed a military officer and eight soldiers in central Syria, another signal that disaffected troops are taking a larger role in the antigovernment uprising and pushing it into more violence after months of a brutal government crackdown.

The attack came as an Arab delegation led by the Qatari prime minister met with President Bashar al-Assad in Damascus, Syria’s capital, to press his government to negotiate with the street protesters and end the conflict, which the United Nations says has left more than 3,000 dead. Syrian activists reported at least 10 more civilian deaths on Wednesday.

One Syrian official, speaking on the condition of anonymity in Damascus, offered kind words for the delegation’s mission. “We have deep divisions between two sides, so we need a national and serious dialogue to save the country,” the official said.

But in the hours before the meeting, the government telegraphed an intransigent stance, mustering tens of thousands of supporters to rally in the capital for the second time this month. The Syrian satellite television station Addounia showed thousands of demonstrators filling Umayyad Square in the heart of Damascus. They were waving Syrian flags, holding pictures of the president and chanting, “The people want Bashar al-Assad.”