Updated

An official for the non-aligned, U.S.-backed Syrian Democratic Forces says its fighters have launched a battle to capture Raqqa, the de facto capital of the Islamic State group.

SDF political official Rezan Hiddo says the official announcement of the battle will come "within hours."

He says SDF fighters have attacked IS positions on the edges of Raqqa at three points. He spoke to The Associated Press by phone late Monday from northern Syria.

Separately, the activist collective Raqqa Is Being Slaughtered Silently reported that artillery fire had fallen on the city for more than two hours.

The Britain-based Syrian Observatory for Human Rights monitoring group says the autonomous Syrian Democratic Forces has been repairing bridges across the Euphrates River in preparation to attack Raqqa.