China has offered to help Iraq defeat Sunni extremists with support for air strikes, according to Ibrahim Jafari, Iraq's foreign minister.

Wang Yi, Mr Jafari's Chinese counterpart, made the offer to help defeat the Islamic State of Iraq and the Levant, known as Isis, when the two men met in New York at September's UN antiterrorism meeting, Mr Jafari said.

Any Chinese assistance would be outside the US-led coalition. "[Mr Wang] said, our policy does not allow us to get involved in the international coalition," Mr Jafari told the Financial Times in Tehran, where he was attending an anti-extremism conference earlier this week.

China is the largest foreign investor in Iraq's oil sector and stands to lose the billions its state-owned groups have ploughed into the country if the fields are lost to the insurgents. Sinopec operates in Kurdistan, while China National Petroleum Corp has interests in the giant Rumaila field near Basra and in Maysan province near the Iranian border. CNPC has already effectively abandoned oilfields it operated in Syria.

Global Times, the Chinese newspaper, reported this week that Isis crews were dismantling a small refinery, in which a Chinese company has invested, west of Baiji to scavenge equipment for Isis-controlled refineries in Mosul, Iraq's second-biggest city.