US Secretary of State Hillary Clinton said Thursday the United States and its allies would continue efforts to put pressure on the regime of Syrian president Bashar Al Assad, Reuters reports.

Clinton is currently in Greenland for a series of meetings with foreign ministers from several countries. During the discussions, Clinton said Assad "is becoming increasingly isolated." 

"The Syrian government is responsible for all events occurring within its borders," Clinton added. "The U.S. and its allies will look for ways to increase pressure on Assad's regime." 

Clinton's comments follow a sharp escalation in efforts by Syrian President Bashar Al Assad to crush the growing popular revolt against his regime.

The Syrian army shelled residential areas in central Syria on Wednesday, according to witnesses. 

Heavy gunfire was heard as at least three residential neighborhoods were hit by tank fire in the besieged city of Homs, which has been the epicenter of some of the largest anti-government demonstrations in recent weeks.

"There were loud explosions and gunfire from automatic rifles throughout the night and until this morning. The area is totally besieged. We are being shelled," one Homs resident told the Associated Press.

Human rights groups say eighteen were killed in the shelling.

Syrian soldiers and tanks also surrounded the city of Hama on Thursday, witnesses say. Assad's father crushed a Sunni revolt there in 1982, killing some 25,000 in the process.

More than 750 people have been killed and thousands detained since the uprising against Assad's regime began in mid-March.