NEW YORK - While US President Barack Obama is under pressure to rein in Iran's nuclear programme, he is increasingly relying on Iranian fighters in an effort to contain the Islamic State in Iraq and Syria without committing American ground troops, according to a media report.

But American officials still maintain that the United States is not coordinating with Iran, considered one of its fiercest global foes, in the fight against a common enemy.    "That may be technically true. But American war planners have been closely monitoring Iran’s parallel war against the Islamic State, also known as ISIS or ISIL, through a range of channels, including conversations on radio frequencies that each side knows the other is monitoring," The New York Times said in a front page dispatch published Thursday.

The paper said the two militaries frequently seek to avoid conflict in their activities by using Iraqi command centers as an intermediary.    

Four days ago, it was pointed out Iranian troops joined 30,000 Iraqi forces to try to wrest Saddam Hussein’s hometown of Tikrit back from Islamic State control,

Citing many national security experts, the Times said Iran’s involvement is helping the Iraqis hold the line against Islamic State advances until American military advisers are finished training Iraq’s underperforming armed forces.

“The only way in which the Obama administration can credibly stick with its strategy is by implicitly assuming that the Iranians will carry most of the weight and win the battles on the ground,” Vali Nasr, a former special adviser to President Obama who is now dean of the School of Advanced International Studies at Johns Hopkins University. “You can’t have your cake and eat it too - the U.S. strategy in Iraq has been successful so far largely because of Iran.”

The paper said it was Iran that organized Iraq’s militias last August to break a week-long Islamic State siege of Amerli, a cluster of farming villages whose Shia residents faced possible slaughter, while American bombs provided support from warplanes.

Administration officials, it said,  were careful to note at the time that the United States was working in Amerli with its allies - namely Iraqi Army units and Kurdish security forces. A senior administration official said that “any coordinating with the militias was not done by us; it would have been done by the I.S.F.,” a reference to the Iraqi security forces.

"It was also Iran’s Quds Force that backed Iraq’s militias and Iraqi security forces in November to liberate the central city of Baiji from the Islamic State, breaking the siege of a nearby oil refinery,"  the Times pointed out. (A month later, the Islamic State took back a part of the city.)

And last summer, when Islamic State militants first captured Mosul and got within striking distance of the Kurdish capital, Erbil, the head of Iran’s Quds Force, Maj. Gen. Qassim Suleimani, flew to Erbil with two planes full of military supplies, American and regional diplomats said. The Iranian move helped to bolster Kurdish defences around Erbil, the officials said.

In Tikrit this week, Iranian-backed militia leaders said that their fighters made up more than two-thirds of the pro-government force of 30,000. They also said that General Suleimani, the Iranian spymaster, was helping to lead from near the front line.

Websites supporting the militias circulated photographs of General Suleimani on Wednesday drinking tea on what was said to be the front line, dressed in black and holding his glass in one hand and a floral patterned saucer in the other.

The presence of General Suleimani - a reviled figure in American security and military circles because he once directed a deadly campaign against American forces in Iraq - makes it difficult for the United States to conduct airstrikes to assist in the Tikrit operation, as it might like, foreign policy experts said.

“There’s just no way that the U.S. military can actively support an offensive led by Suleimani,” said Christopher Harmer, a former aviator in the United States Navy in the Persian Gulf who is now an analyst with the Institute for the Study of War. “He’s a more stately version of Osama bin Laden.”

Appearing before the Senate Armed Services Committee on Tuesday, Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, said that the involvement of Iranian-backed Shias in Tikrit could be “a positive thing” provided it did not exacerbate sectarian tension.

“This is the most overt conduct of Iranian support, in the form of artillery and other things,” General Dempsey said. “Frankly, it will only be a problem if it results in sectarianism.”

Meanwhile, Rafid Jaboori, a spokesman for the Iraqi Prime Minister Haider al-Abadi, said in an interview Wednesday that Iraq had urged the United States and Iran not to play out their bilateral conflict in Iraq’s battle against the Islamic State.

“So far in general there was no clash within the two,” Jaboori said.

He drew a comparison to World War II. “Countries with different ideologies, different priorities, different systems of government, cooperated to defeat the Nazis,” he said. “It’s foreseeable that we see countries which might not get along very well in terms of their bilateral relations working to help Iraq to defeat this threat.”