US warplanes shot down an Iranian drone inside Iraqi airspace north of Baghdad last month, an American military spokesman said on Monday.

"This was not an accident on the part of the Iranians," the unnamed spokesman said in a statement, without elaborating.

"The Unmanned Aerial Vehicle (UAV) was in Iraqi airspace for nearly one hour and 10 minutes and well inside Iraqi territory before it was engaged." The drone was about 60 miles (100 kilometres) from Baghdad, he said.

"Coalition multi-role jet fighters shot down an Iranian UAV February 25," the statement said.

"The pilots were directed to shoot the UAV down after determining there would be no possibility of collateral damage. The UAV was believed to be an Iranian 'Ababil 3' model UAV."

Iraqi defence ministry spokesman Brigadier General Mohamad al-Askari told AFP the drone had been shot down close to the main US air base in Iraq at Balad, some 45 miles (70 kilometres) north of the capital.

"The drone travelled about 130 kilometres (80 miles) through Iraqi airspace," he said.

The report came at a time when Washington is tentatively seeking to unfreeze relations with Tehran, which has made no comment on any drone incident in Iraqi airspace.

US President Barack Obama has pledged to offer diplomatic engagement with US foes, including Iran, to test if there might be scope for negotiated solutions to conflicts.

Last week, however, Obama said he had extended one of the many levels of sanctions against Iran, imposed in 1995 over charges that Tehran dealt in terrorism and sought weapons of mass destruction.

And Washington remains cautious about the growing ties between the two Shiite-majority neighbours, repeatedly accusing Iranian-linked groups of attacking US troops in Iraq.

It also worries about Tehran's future influence on the now Shiite-dominated government in Baghdad as relations strengthen.

Under executed president Saddam Hussein's Sunni-led regime, Tehran and Baghdad fought a devastating 1980-1988 war in which around one million people died.