“We would welcome a common platform for collective action against the terrorists”, he added, dubbing Assad’s forces the “one legitimate conventional army” in Syria.

Iranian President Hassan Rouhani called for the countries of the world to join in a “united front against extremism and violence”, in order to create stability, peace and diplomacy in the Middle East.

Iran needs $150 billion of investment to reach 8 per cent growth a year and lower youth unemployment, President Hassan Rouhani said in an address to Iranian-Americans in New York on Saturday.

“I can now proudly announce that today a new chapter has started in Iran’s relations with the world”, Rouhani said from the floor of the General Assembly.

After a harsh broadside against Saudi Arabia, which Iran has blamed for the death of almost 800 Muslim pilgrims last week – more than 130 of them Iranian – Rouhani hit Israel for its policies on Palestinians and blamed the US for the rise of the Islamic State in Iraq and Syria.

‘Upon arrival to New York, the president has been following up the Mina incident and the news about Iranian Hajj pilgrims who were killed or injured.

Months ago Iran produced a proposal to end the Syrian conflict, which has claimed more than 250,000 lives, and Rouhani said it is still under discussion with some unnamed countries.

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.

The sudden military build-up in support of Assad and a refugee crisis that has spilled over from the region into Europe have lent urgency to attempts to resolve the Syria conflict.

The pilgrims were taking part in a “grand and global spiritual gathering of the haj” but “fell victim to the incompetence and mismanagement of those in charge”, said Mr Rouhani.

Playing down expectations, he said “I have yet to hear directly from the Iranians on anything direct. We’ve had some conversations but… we’ll wait and see where we are”.

“If the Syrian government is taken out of the equation, the terrorists will enter Damascus” and “the whole country will become controlled territory, a safe haven for terrorists,” he said.

Extremists, particularly Daesh militants, have been operating in Syria and Iraq, committing horrendous acts of violence in the Arab countries. They also follow a surprise Russian military buildup in Syria, a longtime ally, to help Assad’s government combat the Islamic State, a move that has raised serious concerns in Washington.

In a separate meeting, President Rouhani told Turkish Prime Minister Ahmet Davutoglu that Tehran and Ankara should forge closer cooperation on different fronts.