Tens of thousands of Syrians have rallied against the government, as security forces expand their crackdown on dissent.

Witnesses and activists say at least 15 people were killed on Friday after forces used live ammunition on protesters. They say most of the deaths occurred around Damascus.

Anti-government protesters also rallied in cities that include Homs, Dara'a, Deir el-Zour and Qamishli. The demonstrations unfolded on the first Friday of the Muslim holy month of Ramadan.

Meanwhile, more details are emerging about the situation in Hama, a city that has been under a military siege since Sunday. A political activist in the city told VOA on Friday that government forces have been carrying out indiscriminate arrests and killings as they storm homes of activists. But he says anti-government demonstrators rallied on Friday in spite of the crackdown.

State-run media reports say the government is working to restore security in Homs, after “armed terrorist groups” carried out acts that include killings and sabotage.

The government has blamed much of the violence in Syria on what it says are terrorists and militants. The state-run SANA news agency said Friday that unidentified gunmen had ambushed a security patrol near the town of Maarat al-Numan, killing two officers.

There is mounting international pressure against President Bashar al-Assad's violent crackdown.

In a statement Friday, U.N. human rights experts urged Syria to stop the killings and “pursue dialogue through peaceful processes.”

Also Friday, the leaders of the U.S., France, and Germany condemned the continued use of “indiscriminate violence” against protesters. A White House statement said Barack Obama spoke separately with Nicolas Sarkozy and Angela Merkel, and the three agreed to consider additional ways to support the Syrian people and bring pressure against Mr. Assad.

On Thursday, U.S. Secretary of State Hillary Clinton said Washington believes more than 2,000 people have been killed in the months-long crackdown. She appealed for a “louder, more effective” international response to the violence.

President Assad issued a decree Thursday that would allow opposition parties to operate for the first time. The move would be a departure from Syria's single-party system that has been dominated for decades by the Assad family's Ba'ath party.