BEIRUT, Lebanon - Syrian President Bashar al-Assad issued a general amnesty Tuesday for prisoners that includes those deemed to have committed political "crimes," as pressure built from a 10-week-old uprising that his regime has failed to quell with overwhelming military force.

The offer was swiftly rejected by the opposition as just another plot by the regime to gain time.

Syrian state television said the amnesty covered "all members of political movements," including the outlawed Muslim Brotherhood, which led an armed uprising against Assad's father in 1982. Membership in the party is punishable by death.

The amnesty could affect about 10,000 people who Syrian activists say have been rounded up since the protests against the Assad regime broke out in mid-March. The release of political prisoners has been a key demand of the opposition.

The offer came as members of the Syrian opposition gathered in Turkey for a conference aimed at overcoming differences and bolstering the protesters who have endured a bloody crackdown that has killed more than 1,000 civilians.

The opposition was quick to reject it.

"This shows weakness on the part of the regime," said Mohammad Abdullah, a Washington-based Syrian dissident who was attending the conference in Antalya, Turkey.

Abdullah, whose father, Ali Abdullah, is a well-known political prisoner, said the move would have been a good one had it come in the first week of the uprising, not after hundreds of protesters had been killed.

"The opposition now will accept nothing less than regime change," he said.

In Washington, the Obama administration expressed doubts over the amnesty offer and demanded that Assad prove to a skeptical world that he was serious about reform.

"He's said a lot of things in recent weeks and months, but we've seen very little concrete action," State Department spokesman Mark Toner told reporters. "It just underscores the fact that he needs to take concrete steps, not rhetoric, to address what's going on in the country."

Meanwhile, army troops pounded a town in the country's turbulent heartland Tuesday with heavy machine guns and artillery in renewed attacks that killed at least one person and wounded many, activists said.

The Local Coordination Committees in Syria, which helps organize and document the country's protests, said that many others were wounded in the attack on Rastan, a town a few miles north of the central city of Homs, which has been under attack since Sunday.