The US ambassador in Baghdad said on Saturday that the State Department has asked for a $6.2 billion budget for Iraq in 2012, underscoring that its oil and gas reserves were critical for the world's future energy needs.

"This country is on a glide path to increase its oil exports," James Jeffrey told reporters at the sprawling US embassy in Baghdad, the world's largest.

The embassy plans to double in size next year to 16,000 personnel, when it takes over many military tasks after US troops pull out of Iraq at the end of this year, including military sales and training of Iraqi security forces.

Nearly 50,000 American troops still remain, down from a high of 170,000 after the 2003 US-led invasion.