In an interview with CBS television, Mr Putin said the Syrian president’s troops were “the only legitimate conventional army there”.
Iraq has long had close ties with neighbouring Iran and has co-ordinated with Tehran in fighting the advance of ISIL – which controls about a third of Iraq and Syria in a self-declared caliphate.
But even though the US and its allies, Russia, Iran, Iraq, the Kurds and Syria all have an urgent need to defeat ISIS, their competing interests make a solution hard to achieve.
The sudden military build-up in support of Mr Al Assad and a refugee crisis that has spilled into Europe have lent new urgency to resolving the Syria war.
Meanwhile, French President Francois Hollande said with his nation’s first airstrikes it “struck in Syria this morning an Islamic State training camp which threatened the security of our country“. It calls for the formation of a transitional government with full executive powers “on the basis of mutual consent”, leading to elections, and would require Assad to relinquish power at some unspecified point.
Besides the crisis in Syria, USA officials say Obama and Putin will discuss the simmering conflict in eastern Ukraine, where the Kremlin is accused of backing pro-Russian separatists.
Russian Foreign Minister Sergei Lavrov and US Secretary of State John Kerry met on Sunday to prepare the ground for the presidents’ meeting. “We’ve always said that this is our sister country”.
The United States has a $500mn programme to train and equip vetted moderates recruited from among the rebels fighting Assad, but it has faced repeated setbacks.
Russian news agency Interfax quoted a military diplomatic source in Moscow as saying the Baghdad coordination centre would be led on a rotating basis by officers of the four countries, starting with Iraq.
Mr Cameron said he hoped to build on the summer signing of an global deal on Iran’s nuclear programme to bolster regional support for a political settlement in Syria.
“If we are to succeed in defeating terrorism, the government in Damascus can not be weakened”, Mr Rouhani said. “Instead of waiting for them to return back home we should help President al-Assad fight them there, in Syria”.
Saudi Arabia is part of a US-led coalition that began an air campaign against ISIL in Syria last September, and insists it will never cooperate with the Assad regime.
The Prime Minister will use one-to-one talks with a number of key figures – though not Mr Putin – to press his case that the Syrian president “can’t be part” of a peaceful solution to the civil war. Since most Syrians want to rid themselves of the dictator, most recruits are from neighboring countries. First of all, the Iranians have no say in the matter.