The US military intervened to keep Iraqi troops out of Baghdad International Airport today after a British security company grounded civilian flights to force the Iraqi Government to settle six months of unpaid bills.

The London-based Global Strategies Group has looked after security at the airport, Iraq's main link to the outside world, since June 2004, but the $4.5 million-a-month contract it agreed with the now defunct US Coalition Provision Authority has lapsed.

Global closed the airport this morning after lengthy negotiations on the contract failed to produce any payments. Its move infuriated the Government, which said it was sending in troops to take over the airport and get flights moving again.

Esmat Amer, the acting Transport Minister, told Reuters: "My forces have entered the airport. The airport is not closed. We are taking some technical measures now and will soon resume the flights, maybe in the next few hours... It is a matter of sovereignty for us."

But Giles Morgan, a Global spokesman, told Times Online that Iraqi troops had not entered the airport and would not in any case be qualified to screen passengers and baggage. He said that the US military, which also uses the airport and works closely with Global, had put extra troops on the first checkpoint on the main road to the airport to head the Iraqis off.

"There was a statement by the Ministry of Transportation earlier that Iraqi troops were going in, but it is my understanding that the Americans put troops on Checkpoint One and insisted that the Iraqis are not going in," Mr Morgan said. He said the Iraqi order to enter the airport had been quickly countermanded.

Global is one of a number of Western firms employed under lucrative outsourcing arrangements to run key infrastructure and security projects. It employs some 2,000 staff in Iraq, mostly former Gurkhas, soldiers from Fiji and expatriate Britons, and is also responsible for security in the Baghdad Green Zone, which houses Government and Coalition offices.

At the airport, formerly Saddam International Airport, Global has around 550 staff, who guard the airport against insurgent attack as well as providing the security and ground staff for the civilian flights. There are about 15 civilian flights a day out of the airport operated by Iraqi Airways, Royal Jordanian Airlines and three companies operating out of the United Arab Emirates - Jobotier, Ishtar and Tigris airlines.

Mr Morgan said the Americans were concerned that a large influx of troops would threaten the security of the airfield and its airspace. The company continues to secure the airport perimeter.

In a statement, the company said: "Global has been in constant negotiations with senior members of the Iraqi Government, which is currently not paying the company. Once payment has been made by the client, Global will resume its work and thus allow normal air operations to resume."

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