Gunfire was reported Tuesday in the flashpoint Syrian town of Daraa, as a military siege there to end pro-democracy protests entered its second day.
The crackdown with tanks and troops showed no signs of easing amid an international outcry over violence against demonstrators. Residents are reportedly too afraid to venture out in Daraa. Human rights groups also report dozens of people are being detained by Syrian forces nationwide.
Witnesses and human rights activists say at least 20 people were killed Monday when hundreds of Syrian troops and tanks entered Daraa to quell demonstrations.
Britain's Foreign Secretary William Hague is urging Syria to end the crackdown, adding that his country is working with its international partners to persuade Syrian authorities to respect basic and universal human rights.
The United States has condemned the violence against Syrian citizens, calling it "completely deplorable."
The State Department has issued a travel warning advising U.S. citizens and non-emergency embassy personnel to leave Syria while commercial transportation is still available.
More than 350 people have been killed during Syria's crackdown since pro-democracy protests erupted last month.
President Bashar al-Assad last week ended the country's 48-year-old emergency law - a key demand of protesters - and abolished a state security court. But the government then took other steps to crush demonstrations.