BEIRUT (AP) — Syrian activists say government forces are keeping up their pressure on the country's strategic southwest, using artillery, airstrikes and barrel bombs to target rebel-held parts of the region.

The Britain-based Syrian Observatory for Human Rights says government helicopters have dropped more than 12 barrel bombs in the province of Daraa so far on Friday. It's the first use of the rudimentary and non-discriminatory weapons in the region in over a year.

Last July, the United States, Russia and Jordan negotiated a truce for the region, which borders Jordan and the Israeli-occupied Golan Heights.

The calm began to unravel in recent weeks, prompting U.S warning of "serious repercussions" for truce violations. Washington didn't elaborate.

The Observatory said 16 people have been killed in government strikes since Tuesday, including nine children.