Syria: Helicopters, tanks reportedly used in assault on Deraa (VIDEO)

Syrian troops on Sunday stormed Deraa, the city at the center of the six-week anti-government protest, using helicopters for the first time in an apparent act of intimidation, witnesses said.

And tanks fired shells into the heart of Deraa's ancient Roman quarter, a resident who lives on the outskirts of the city told the Guardian, saying he could identify the weaponry because he was a former soldier.

Troops also seized control of a mosque in Deraa on Saturday, according to the Washington Post, a day after the Obama administration imposed fresh sanctions targeting on three top Syrian officials, Syria's intelligence agency and Iran's Revolutionary Guard.

Meanwhile, anti-government protesters were planning further demonstrations during the week, apparently undaunted by a violent security crackdown that human rights groups said killed 66 Friday during nationwide protests against at the center of the uprising against President Bashar al-Assad's one-party rule.

Videos posted on YouTube and obtained by satellite television showed bodies in the streets of the city of Homs and in a southern village, apparently after troops had opened fire on protesters the day before.

Activists said the "week of breaking the siege" protests would begin in Deraa on Sunday and around the capital, Damascus, on Monday, Al Jazeera reported.

They were referring to the brutal lockdown imposed on the southern city of Deraa and in the Damascus suburb of Douma by security forces.

Deraa, under siege by the Syrian army since Monday, has reportedly been without fuel, water, and power for six days.

Syrian activists say six civilians were killed in Deraa on Saturday, when the military and snipers opened fire, and that a woman and her two daughters were among those killed when a tank shell hit their home, VOA reports.

Reports from the town Saturday said that the Syrian military had overrun the Omari mosque in the heart of the old city where regime opponents had taken refuge, turning it into a makeshift hospital for those injured in the assault.

The Associated Press quoted a resident contacted by phone as saying soldiers were backed by tanks and three helicopters in the attack. The use of helicopters, which could not be independently confirmed, would mark a first in the effort to suppress the Syrian uprising. 

In another development in the Deraa region, 138 more members of Assad's Baath party resigned in protest against the government's crackdown, VOA reports. En masse, 200 Baath Party resigned earlier in the week.

Syrian Prime Minister Adel Safar announced plans for more reforms on Saturday, in an apparent bid to appease opposition activists. Assad recently lifted the country's almost 50-year-old emergency law — a key demand of protesters.

However, Syrian human rights groups say at least 560 civilians have been killed by the country's security forces since the anti-government protests erupted six weeks ago.

In Washington's first concrete steps in response to a bloody crackdown on protests, the U.S. imposed sanctions that freeze any assets those targeted have in U.S. jurisdictions and bar Americans from business with them.

Bashar, Syria's long-serving ruler, was not among those targeted but could be named soon if violence by government forces against democracy protesters continued, a senior U.S. official said, Reuters reported.