“We hold the Syrian leadership fully responsible for their heinous act aimed at spreading chaos throughout the country.”

The letter was signed by Sheikh Kareem Rajeh and prominent Damascene preacher Mouaz Al Khatib, a major figure in Syria’s pro-democracy uprising, and Jawdat Said, a well-known Islamic scholar.

The Syrian army has intensified crackdown on pro-democracy protesters at the start of Ramadan, killing dozens of civilians across the country.

Activists said security forces have killed more than 150 people in the past two days and tanks shelled residential areas in Hama, the country’s fourth-biggest city. They said that the figures might even be higher.

“Ten martyrs fell and several people were wounded by gunfire from security forces during protests in several Syrian towns after the ‘taraweeh’ evening prayers” on Monday’s first day of Ramadan, Syrian Observatory for Human Rights chief Rami Abdel Rahman said, according to AFP, adding that the day’s death toll was 24.

The attack on Hama, accounting for the bulk of the deaths, was unleashed at the start of the holy Muslim month of Ramadan on Monday.

On Tuesday at least three people were killed in Hama, including two brothers, when a rocket hit their car, and the third person was killed by a sniper, Syrian Observatory for Human Rights chief Rami Abdel Rahman said.

He also reported a “massive deployment of tanks on the road between Homs and Ruston” in central Syria where he said residents “are worried that the army is preparing to launch an operation.”

On Tuesday night, there were demonstrations in Homs and numerous villages in the vicinity, as well as in the coastal city of Latakia and Baniyas.

Homs, Syria’s third city, is due south of Hama, where an estimated 20,000 people died when the government of Assad’s father, Hafez, put down an Islamist revolt in 1982.