Iraq has said that its military officials are engaged in intelligence and security cooperation in Baghdad with Russia, Iran, and Syria to counter the threat from the Islamic State of Iraq and the Levant (ISIL), a pact that could raise concerns in the US.

A statement from the Iraqi military's joint operations command on Saturday said the cooperation had come "with increased Russian concern about the presence of thousands of terrorists from Russia undertaking criminal acts with [ISIL]".

The move comes as at the same time Russia has stepped up its military involvement in Syria in recent weeks, while pressing for Damascus to be included in international efforts to fight ISIL, a demand Washington rejects.

The announcement also reflects Iran's increasing influence just four years after the withdrawal of US troops from Iraq.

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.

The source added a committee might be created in Baghdad to plan military operations and control armed forces units in the fight against ISIL.

Iraqi officials on Friday had denied reports of a coordination unit in Baghdad set up by Russian, Syrian, and Iranian military commanders aimed at working with Iranian-backed Shia militias in Iraq.

The armed groups, some of which have fought alongside troops loyal to Syrian President Bashar al-Assad, are seen as a critical weapon in Baghdad's battle against ISIL.

Iraqi Foreign Minister Ibrahim al-Jaafari said in New York on Friday that his country had not received any Russian military advisers to help its forces but called for the US-led coalition to bomb more ISIL targets in Iraq.

Russian demand

Despite more than $20bn in US aid and training, Iraq's army has nearly collapsed twice in the last year in the face of advances by ISIL, which controls large swaths of territory in the north and west, as well as in Syria.

Western officials have said US Secretary of State John Kerry wants to launch a new effort at the UN General Assembly this week to try to find a political solution to the Syrian conflict.

Diplomacy has taken on new urgency in light of Russia's military build-up in support of Assad and a refugee crisis that has spilled into Europe.

Critics have urged US President Barack Obama to be more decisive in the Middle East, particularly towards the Syrian conflict and say lack of a clear US policy has given ISIL opportunities to expand

A Russian foreign ministry official told Interfax on Friday that Moscow could "theoretically" join the US-led coalition against ISIL if Damascus were included in international efforts to combat the armed group and any international military operation in Syria had a UN mandate.