An advance team of six United Nations observers has begun monitoring a four-day-old cease-fire in Syria even as the truce appeared to be unraveling with activists reporting at least 14 civilians killed by security forces in a continuing crackdown on a year-long uprising.

The Britain-based Syrian Observatory for Human Rights told VOA the civilians were killed Monday in government attacks across the country, including a third day of artillery strikes on rebel-held neighborhoods of Homs, Syria's third-largest city. The group says several civilians also were killed in attacks in the northern region of Idlib and the central region of Hama. The casualties could not be independently verified.

A Moroccan U.N. observer said he was “optimistic” about prospects for the shaky cease-fire as he and other members of the advance team began talks with Syrian officials in Damascus. The six unarmed U.N. soldiers arrived in Syria late Sunday. Moroccan Colonel Ahmed Himmiche said they will work to achieve their goals “as soon as possible.”

A spokesman for international envoy Kofi Annan said the advance team “will start with setting up operating headquarters and reaching out to the Syrian government and opposition forces so both sides fully understand the role of the U.N. observers.” He said an additional 25 monitors are expected to arrive within days.

U.N. Secretary-General Ban Ki-moon said Monday the Syrian government has a “responsibility” to ensure that the observers can move freely to monitor the truce, which took effect last Thursday as part of a U.N.-backed peace plan approved by Damascus. Mr. Ban also urged Syrian security forces to exercise restraint and called on rebels to fully cooperate with the cease-fire, which he acknowledged is “very fragile.”

The U.N. Security Council approved the deployment of 30 observers to Syria in a resolution adopted unanimously on Saturday. Mr. Annan has called for the monitoring team to be expanded to 250 personnel, but a second Council resolution is required for such a step.

The U.S. ambassador to the United Nations, Susan Rice, said Monday that if Syria's violence persists despite the cease-fire, “it will call into question the wisdom … of sending in the full monitoring presence.”

U.N. human rights investigators said Monday they have gathered evidence of Syrian government attacks on civilian areas since the truce began. The Geneva-based Commission of Inquiry on Syria said Syrian security forces have shelled the Khaldieh district of Homs and used heavy weapons in the regions of Idlib and the Damascus suburbs.

The panel appointed by the U.N. Human Rights Council also said it continued to receive reports of human rights abuses committed by anti-government groups.

Meanwhile, members of a Syria-based opposition group opposed to foreign intervention in the uprising met with Russian officials in Moscow on Monday. Representatives of the National Coordination Committee described the talks as positive and said they agreed with Russia on supporting the U.N.-backed Syria peace plan, drafted by Mr. Annan.

The Syria-based group has rejected calls by the exiled Syrian National Council for foreign nations to arm the rebels fighting to end President Bashar al-Assad's 11-year autocratic rule.

The United Nations estimates that more than 9,000 people have been killed since the anti-Assad revolt began over a year ago.