Unrelenting bloodshed in Syria yesterday greeted UN observers sent to monitor a fragile so-called truce.

The Syrian Observatory for Human Rights, relaying reports from activists, said at least two people were killed and dozens wounded by shelling as troops sought to take control of the town of Basr al Harir in the southern province of Deraa.

In the northern province of Idlib, Government forces fired mortars and machine guns in two villages, killing three people, the Observatory said.

It said they also shelled the Khalidiya and Bayada districts of Homs, where their artillery assault resumed on Saturday, two days after the truce came into force. Streets of Homs held by rebels earlier this year now resemble scenes from World War Two.

The reported violence, a day after the Observatory said 23 people were killed, greeted a UN team of six soldiers on their second day preparing for a mission of 250 observers to check compliance with the truce.

Syrian leader Bashar al Assad, who agreed a peace plan with UN-Arab League Kofi Annan three weeks ago, has apparently ignored its primary demand – that tanks, troops and heavy weapons be withdrawn from populated areas and all violence cease.

UN human rights investigators said they had received reports of shelling and arrests by Syrian forces since the ceasefire, as well as executions of soldiers captured by rebel forces.

The US envoy to the United Nations, Susan Rice, said the realities on the ground could jeopardise plans to extend the monitoring mission, charged with overseeing an end to 13 months of violence.

"Should the violence persist and the ceasefire not hold, that ... will call into question the wisdom of sending in the full monitoring presence," she said.