The company that polices Baghdad's airport closed it to passengers on Friday for the second time in three months, in another attempt to force the Iraqi government to pay what it says are months of unpaid bills.

A senior spokesman for Iraq's Transport Ministry confirmed the airport was closed over the money issue but said: "Within hours we will solve the problem... We will pay them."

"We haven't been paid for seven months," Giles Morgan, a spokesman for Global Strategies Group, which has guarded the airport with about 550 staff since the middle of last year.

He could not say how long the stoppage would last. Similar action in June closed the Iraqi capital's main link to the outside world for two days.

A US military spokesman said the military was unaffected and Morgan said security measures were still fully in place.

"Global has been in constant negotiations with senior members of the Iraqi government, which is currently not paying the company," Global said in a statement.

"Once payment has been made by the client, Global will resume its work and thus allow normal air operations to resume."

Global has some 2,000 security personnel in Iraq, one of many private companies providing services to the military, government and private organizations.

Many of Global's guards are Nepalese former soldiers with British Gurkha units. About a third of Global's staff at the airport are Iraqi, Morgan said.

With insurgent attacks on roads around the city, Baghdad Airport is the capital's main link to the outside world.

It is in near constant use by the US and British military as well as commercial operators, with about 50 commercial flights a day.

Iraqi Airways has been revived in the past few months after being grounded for more than a decade by sanctions and war.