UNITED NATIONS: The United States warned Monday that heightened violence in Syria threatens the sending of a full UN ceasefire observer mission.

The US ambassador to the United Nations, Susan Rice, said new attacks by government forces “call into question the wisdom and viability” of sending the full 200 international monitors.

The first six unarmed UN military observers started work in Damascus on Monday. The UN Security Council has said, however, that the full force cannot go if there is a safety threat.

“We are gravely concerned ... that the violence continues, that the government seems to continue, if not in recent days intensify, bombardment in Homs in particular,” Rice told reporters.

The government violence was “unacceptable” and against commitments made to UN-Arab League envoy Kofi Annan, she added.

Should the cessation of hostilities started last Thursday collapse the United States and the UN Security Council believe “it will call into question the wisdom and viability of sending in the full monitoring presence,” Rice said.

A UN Security Council resolution passed on Saturday approved only an advance mission of 30 observers. The full force will require a new UN resolution.

Syrian forces shelled the flashpoint city of Homs on Monday and killed 12 civilians in battles with rebels in Idlib, activists said.