Syrian security forces have shot and killed at least 15 people as they conducted raids and fired on protesters who flooded streets after Friday prayers.

Syrian activists say most of the killings took place in the northwestern region of Jabal al-Zawiya, in the southern province of Deraa and the central province of Hama.

The London-based Syrian Observatory for Human Rights says at least two of the deaths were in the central city of Homs.

The violence follows United Nations Secretary-General Ban Ki-moon's call for a “coherent” international response to Syria's violent crackdown against dissent, as the uprisings entered their seventh month.

Mr. Ban Thursday accused Syrian President Bashar al-Assad of “escalating violence and repression” and ignoring appeals to stop state-sponsored violence. The U.N. chief said “enough is enough” regarding Mr. Assad's broken promises of reform.

On Friday, Turkish Prime Minister Recep Tayyip Erdogan joined the chorus of condemnation against the violence in Syria. Mr. Erdogan predicted the fall of the Assad government, saying the era of oppressive dictators is past.

Thursday, Syrian opposition activists announced in Istanbul, Turkey, the formation of a council to present a united front against Mr. Assad. They said the council includes 140 members, with half of them living in Syria.

The United States expressed its support, but noted the need for coordination as the group faces many challenges.

U.S. officials urged Americans to immediately leave Syria, repeating their warning issued last month.

The United Nations estimates that 2,600 people have been killed in Syria's six-month uprising against Mr. Assad's 11-year autocratic rule. The Syrian government said Monday about 1,400 have been killed, half of them security personnel.