The head of the UN Stabilization Mission in Syria (UNSMIS) says the mission has been suspended because of escalating violence, agencies report.

On Friday, the Norwegian Gen Robert Mood said there appeared to be a "lack of willingness" from Syria's government and opposition to seek peace.

He also said violence had intensified in the preceding 10 days, putting his unarmed observers at significant risk.

Earlier, activists said troops had been shelling parts of Homs and Damascus.

At least seven people were killed overnight in Douma, an eastern suburb of the capital, while at least 18 others died in violence elsewhere, the UK-based Syrian Observatory for Human Rights reported.

In a statement announcing the suspension of UNSMIS operations, Gen Mood said: "The observers will not be conducting patrols and will stay in their locations until further notice."

The mission's 298 military observers and 112 civilian staff are in Syria to verify the implementation of the six-point peace plan negotiated by the UN and Arab League envoy, Kofi Annan, which included a ceasefire.

On Friday, Gen Mood told a news conference in Damascus that after the mission began on 29 April there had been a lull in violence, "brought about willingly" by the government and rebels.

But he warned: "Violence over the past 10 days has been intensifying, again willingly by both parties, with losses on both sides and significant risks to our observers."

"The Syrian population, civilians, is suffering and in some locations, civilians have been trapped by ongoing operations."

The general noted both sides had accepted Annan's plan, but said: "There appears to be a lack of willingness to seek a peaceful transition.

"Instead there appears to be a push towards advancing military positions," he added.

Gen Mood warned that the UN mission was not open-ended and would be under review as it neared the expiry of its current mandate in July. But he hinted that it should be strengthened in numbers and equipment.

The UN says at least 10,000 people have died since pro-democracy protests began in March 2011. In April, the Syrian government reported that 6,143 Syrian citizens had been killed by "terrorist groups".