Violence sweeping across Syria killed 25 people on Saturday, most of them in a battle between troops and a growing force of Army defectors who have joined the movement to oust the ruler, President Bashar Assad, activists said.

The revolt against Mr. Assad’s rule began with peaceful protests in mid-March, triggering a brutal crackdown. The unrest has steadily become bloodier as defectors and some civilians take up arms, prompting the United Nations’ human rights chief to refer to it this week as a civil war and urge the international community to protect Syrian civilians.

Economic and diplomatic sanctions by the United States, the European Union, Turkey and the 22-member Arab League have so far failed to blunt the turmoil. Arab officials were to meet on Saturday in the Gulf nation of Qatar to review punitive steps by the Arab League, including a travel ban on 17 Syrian officials, among them Cabinet Ministers and security officers.

Many of the sanctions announced last Sunday by Syria’s Arab neighbours went into effect immediately, including cutting off transactions with the Syrian central bank, halting Arab government funding for projects in Syria and freezing government assets.

The worst violence on Saturday took place in the restive northwestern city of Idlib.

The pre-dawn clashes between regime forces and defectors killed seven soldiers and policemen, as well as five defectors and three civilians, according to a British-based group of Syrian activists called the Syrian Observatory for Human Rights.

Elsewhere, security forces killed one civilian in the southern province of Daraa, six in the central region of Homs and three others in areas near Idlib, the observatory said.

The U.N.’s top human rights official said this week that Syria is in a state of civil war and that more than 4,000 people have been killed since March.

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