Syrian forces were locked in fierce gunfights yesterday with rebels in one city and shelled another, as the UN chief urged “maximum restraint” after the arrival of observers to oversee a truce aimed at ending 13 months of bloodshed.

President Bashar al-Assad’s forces killed 12 civilians and were fighting rebels at Idlib in the northwest, while also shelling the flashpoint central city of Homs, said the Syrian Observatory for Human Rights.

Since a UN-backed ceasefire came into force at dawn on Thursday, at least 55 people, mostly civilians, have been killed in violence that prompted UN chief Ban Ki-moon to urge Syria to ensure the truce does not collapse.

The Observatory said yesterday that 11,117 people have been killed in 13 months of unrest – 7,972 civilians and 3,145 military and gunmen, including fewer than 600 rebel fighters.

In Brussels, Mr Ban called on Damascus to exercise “maximum restraint” and the opposition to “fully cooperate” to cement the shaky ceasefire.

An advance team of six international observers arrived in Damascus late on Sunday, the UN said.

The delegation – the first of 30 monitors the UN Security Council approved on Saturday – will set up a headquarters and prepare routines to verify a cessation of hostilities. Their mission is just one part of the six-point peace plan that Syria agreed with UN-Arab League envoy Kofi Annan.

The former UN chief wants more than 200 observers to be deployed in Syria, but the Security Council has said there would be a full mission only if the violence halts.

The observers were welcomed by Syria, which hoped they would see for themselves the “crimes” committed by “armed terrorist groups,” said the state news agency Sana.

They face a perilous task, with Western nations doubting Mr Assad’s commitment to the ceasefire amid reports his forces have kept battering rebel strongholds and clashed with rebels.

A spike in deadly violence forced the Arab League to end its own Syrian monitoring mission in late January, barely a month after sending observers.

Yesterday, security forces killed two civilians when they fired on a car in Hama, while a third passenger later died of wounds, said the Observatory.

In the same province, security forces killed a 16-year-old youth after it opened fire at random in the village of Khatab, said the Observatory.

Elsewhere, fierce gunfights broke out at dawn between forces loyal to Assad and rebels in the northwestern city of Idlib, is said.

Four civilians were shot dead by security forces during the gunfight.

Security forces also shot dead a civilian in the town of Inkhel, southern Daraa province, where the uprising against Assad’s iron-fisted rule erupted in March 2011.

Regime forces resumed shelling rebel neighbourhoods of Khaldiyeh and Bayyada in the central city of Homs, a day after at least five civilians were killed there.

Three civilians were killed in the shelling, the Observatory said.

The authorities on Sunday charged that rebels had “intensified” attacks on security forces and civilians, warning of a response, as state media published a list of alleged acts of violence.

Security forces “will prevent the terrorist groups from continuing their criminal attacks,” said a military official quoted by state media, accusing the rebels of a deliberate escalation to wreck the truce.

Mr Ban voiced concern over the shelling of Homs.

“I am very much concerned about what has happened since yesterday and today,” he said. “It is important, absolutely important, that the Syrian government should take all the measures to keep this cessation of violence.”

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