Syrian government shelling of an opposition-held southern region has killed at least six civilians, hours after a US warning not to jeopardise talks on the area's fate, AFP reported Friday (June 15th).

The Syrian Observatory for Human Rights said the casualties, who included two children, were killed in shelling on two villages in the north of Daraa province.

The shelling came from army positions that had recently received reinforcements, the Observatory said.

The US State Department had warned Damascus Thursday against any military action that could scupper ongoing talks aimed at finding a settlement for the complex southern front.

"We reiterate that any Syrian government military actions against the south-west de-escalation zone risk broadening the conflict," spokeswoman Heather Nauert said in a statement.

"We affirm again that the US will take firm and appropriate measures in response to Syrian government violations in this area," she said.

The US, Russia and Jordan agreed to a de-escalation deal in the southern province, and negotiations are continuing in a bid to reach a deal that would remove the need for a government offensive.

Opposition groups, who still control about two thirds of Daraa, have so far refused to negotiate with the Syrian regime.

The regime wants the opposition to withdraw from the area either by force or under a deal similar to those that saw armed groups transferred from their bastions in and around Damascus.