WASHINGTON, USA (AP) — It’s the fog of diplomacy.

For years, Iran has been an arch-enemy of the United States. Now, with alliances blurred in the Mideast, the two countries are talking about how to stop an offensive in Iraq by al-Qaida-inspired insurgents.

How is it that adversaries that haven’t trusted each other for 35 years could cooperate on Iraq today?

They are strange bedfellows, to say the least.

In the Syrian civil war, the US backs the opposition. Iran supports Syrian President Bashar Assad.

The US for three decades has considered Iran a “state sponsor of terrorism.” The US says Iran bankrolls anti-Israel terrorist groups and other extremists intent on destabilising the Middle East.

The US has threatened Iran with military action if Iran approaches the capacity to develop nuclear weapons.

But despite all the differences, the US and Iran are more engaged diplomatically at this moment than in years.

After a breakthrough interim agreement last year, the US, Iran and other nations are hoping to wrap up a deal within the next month that would curb Iran’s nuclear program. Progress on nuclear talks is leading American officials to explore whether Iran can be a useful partner on interests long viewed as shared, such as fighting Sunni extremism and ensuring stability of Iraq.

Iran, like the Iraqi government, is Shiite. The insurgent group leading the assault in Iraq, the Islamic State of Iraq and the Levant, is Sunni.

But there is worry that Iran is trying to leverage its helpfulness on Iraq into better terms in the nuclear negotiations.

“I would be sceptical that cooperating with Iran — particularly sharing sensitive intelligence information — would be in our overall interest,” Sen Mitch McConnell, R-Ky, the Senate minority leader, told The Associated Press.

“In fact, it’s hard for me to conceive of any level of Iranian cooperation that doesn’t lead to future demands for concessions on the nuclear programme, or foment the return of Shia militias and terrorist groups, which is harmful to resolving the sectarian disputes within Iraq,” McConnell said. “Remember, the Iranians are working aggressively to keep Assad in power in Syria.”

His concern was highlighted by the comments this past week by Mohammad Nahavandian, chief of staff to Iran’s president, Hassan Rouhani. The aide suggested nuclear talks and Iraq’s crisis were connected. The State Department rejected

any linkage.

Secretary of State John Kerry, heading to the Mideast this weekend to discuss Iraq’s stability, has fuelled talk about US-Iranian cooperation. He said early last week that the Obama administration was open to discussions with Tehran if the Iranians help end the violence in Iraq and restore confidence in the Baghdad government.

American and Iranian diplomats talked about Iraq on the sidelines of nuclear negotiations in Vienna in recent days. US officials have rejected military cooperation with Iran and thus far, legislative aides said, the understanding in Congress is that no intelligence-sharing mechanism with Tehran has been finalised.

But the comments had officials and lawmakers in Washington and the Middle East abuzz.

At a breakfast this past week with the Senate Foreign Relations Committee, Kerry steered away from questions about how specifically the US might cooperate with Tehran, according to aides, who weren’t authorised to speak about private meetings and demanded anonymity.