At least four people have been killed in Syria when security forces opened fire on protesters who poured onto the streets Friday, in spite of a government crackdown on dissent.

Witnesses and activists say forces used live ammunition and tear gas, as thousands of demonstrators renewed calls for President Bashar al-Assad's resignation. Activists say at least four people were killed near the capital, Damascus.

Protesters have rallied in other cities, including Dara'a, Deir el-Zour and Qamishli. The demonstrations have unfolded on the first Friday of the Muslim holy month of Ramadan.

Meanwhile, the Associated Press says the military has renewed shelling in Hama, a city that has been under siege since Sunday.

There is mounting international pressure against President Assad's crackdown on protests.

U.S. Secretary of State Hillary Clinton said Thursday that 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. Clinton also said the U.S. stands fully behind a U.N. Security Council statement on Wednesday condemning Syrian human rights violations.

But Clinton said more needs to be done to increase the pressure, saying European and Arab countries need to join the United States in imposing additional sanctions against the Syrian government.

The government has blamed much of the violence on what it says are terrorists and militants.

In a conciliatory gesture to anti-government protesters, President Assad issued a decree Thursday to allow opposition parties to operate for the first time. The move is a departure from Syria's single-party system which has been dominated for decades by the Assad family's Ba'ath party.

The U.S. State Department dismissed the announcement as “empty rhetoric.”