Casualties are rushed to hospital Reuters

Syrian forces have fired across the border into Turkey and hit a refugee camp in the latest incident to fuel international concern about escalating violence hours before a UN deadline aimed at ending the crisis.

In the first such incident since Turkey began sheltering thousands of Syrians last summer, five people – three Syrians, one Turkish translator and one Turkish policeman – were wounded inside the camp near the town of Kilis, in south-western Gaziantep province, governor Yusuf Odabas told the Associated Press.

Mohammad Abdelqader, a refugee in the camp who told Reuters he had witnessed Monday's shootings, said two Syrians had been killed and two more had been injured. The report could not be independently confirmed.

Turkey is understood to have immediately protested the shooting and called on Syria to halt the fire.

Location of the camp

Meanwhile, China called on the Syrian government and opposition to comply with a UN-backed plan for a ceasefire and negotiations, as hopes faded that an agreement could be reached by Tuesday morning's deadline.

China called on both sides to abide by ceasefire and troop withdrawal promises, co-operate with Kofi Annan's mediation efforts and "promote a political solution to the conflict".

Annan had called for troops to stand down by Tuesday morning, with a ceasefire taking effect 48 hours later, as the first stage in a six-point international plan for political negotiations between the regime of President Bashar al-Assad and its opponents.

Turkey's deputy foreign minister, Naci Koru, was quoted on Monday as saying the deadline had essentially become irrelevant. "10 April has become void. After Kofi Annan's visit tomorrow [to Turkey] a new stage will start," he was quoted as saying on the website of the Turkish broadcaster NTV.

The mounting concern came as Syria's foreign minister, Walid al-Muallem, flew to Moscow for emergency talks. In February, Russia and China used their vetoes to protect Syria from censure by the UN security council, but since then they have backed the Annan plan.

The UN estimates that 9,000 people have been killed in Syria over the last 13 months. Reports from local activists said 60 people had been killed across the country on Sunday. On Monday, local activists said 30 people - including 17 children - had been killed by security forces during the bombardment of the central town of al-Latmana. Lebanon's Al-Jadeed television channel said one of its cameramen, Ali Shaaban, had been shot dead near the border between the two countries.

Syrian state media said on Monday that Assad's government stood by its commitment to the Annan plan and blamed "armed groups" for failing to provide written guarantees that they would stop fighting before regime forces withdrew from cities.

"Annan has not offered written guarantees to the Syrian government that the armed groups agreed to stop violence, nor has he offered guarantees that Qatar, Saudi Arabia and Turkey will commit to stop funding and arming terrorist groups," the foreign ministry said.

Opposition activists poured scorn on Assad's demand for guarantees and said it was consistent with his strategy of buying time and exploiting the divisions between opponents at home and abroad. But many also blamed Annan for being naive to believe Assad had any intention of compromising. "The Syrian regime has just given Annan the finger," said one.

Annan, the UN envoy and former secretary-general, is reportedly heading to Turkey to inspect refugee camps there.

Human Rights Watch said Syrian security forces had summarily executed more than 100 – and possibly many more – civilians and wounded or captured opposition fighters during recent attacks on cities and towns. It said many of the incidents took place last month.