DAMASCUS, Syria — Protests broke out in four Syrian cities on Friday, the first large-scale demonstrations here since the pro-democracy uprisings began in the Arab world three months ago. Brutal police crackdowns followed, leaving six people dead and scores injured.

In the largest protests, several thousand people gathered in the center of Dara’a, in southern Syria, chanting “God, Syria and freedom only,” witnesses said. They demanded the resignation of the mayor and the leader of the local branch of the security police. The police later opened fire on the crowd, killing six, the witnesses said.

There were also protests in Banias, on the Mediterranean coast; in the central city of Homs; and here, in the capital. A Facebook page, “the Syrian revolution 2011,” has called on people to protest against corruption and repression.

Antigovernment protests are virtually unknown in Syria, a police state where political opposition has been brutally suppressed in the past.