GETTY/REUTERS Syrian President Bashar al Assad is accused of bombing Syrians after this attack in Idlib

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In a dramatic about turn, the Prime Minister was expected to tell the United Nations General Assembly that Mr Assad could remain in power during a transitional government. Mr Cameron hopes the new approach will end the four-year war in Syria and focus attention on the terrorists, who are recruiting hundreds of fighters from Britain every year. In the past, Mr Cameron has accused the Syrian government of killing its own people and committing a “war crime” after at least 1,300 people were killed by chemical weapons near Damascus. Just two years ago, Mr Cameron also tried to launch air strikes against the Assad regime but was thwarted when he lost a Commons vote. Despite agreeing that President Assad could remain in power, Mr Cameron last night called for the dictator to be prosecuted for war crimes.

EPA David Cameron with UN Secretary General Ban Ki Moon in New York yesterday

He said Mr Assad broke international law over the 2013 chemical weapons attack on his own people which killed at last 1,300 Syrians. “He has butchered his own people,” Mr Cameron said. “He has helped create this conflict and this migration crisis. “He can’t play a part in the future of Syria and that position hasn’t changed. People who break international law should be subject to international law.”

REUTERS Assad's forces are suspected of carrying out air strikes on the Syrian town of Idlib

In his speech late last night, he was expected to insist that President Assad quit once a government was elected, but he could stay on for the short term. His hopes for regime change were complicated after Russia’s President Vladimir Putin sent troops and jets to a military base near Latakia in Syria and the port of Tartus.

REUTERS Vladimir Putin (R) gives an interview in Moscow region, Russia

People who break international law should be subject to international law David Cameron

With the Islamic State controlling half of Syria, Mr Cameron now sees defeating the terrorists as the main priority. Last night, Mr Putin offered Mr Cameron an olive branch and raised the possibility of a “grand coalition” between Russia, Europe and the US. The Russian president told US TV network CBS that he wanted to engage in “collective” action against the Islamic State. In another sign of a thaw in relations with the West, he is to address the UN today for the first time in 10 years. There had been speculation that Mr Cameron would not speak and would leave before Philip Hammond, the Foreign Secretary, gave the address.

REUTERS Scores of houses and buildings in Idlib were destroyed in the strikes

REUTERS A blood-stained man walks away from the destruction in Idlib