WASHINGTON, June 22: As President Barack Obama finalises his plan to withdraw up to 30,000 troops from Afghanistan by the end of 2012, the Pentagon indicated on Wednesday that its top commander in that country would also leave earlier than expected.

Pentagon officials told reporters that Gen David Petraeus might leave Afghanistan by mid-July, much sooner than the original September target date for the change of command.

Gen Petraeus will return to Washington to take over the reins of CIA from Leon Panetta who is now going to the Pentagon as the new defence secretary.

Gen Petraeus was tentatively scheduled to leave on July 18, a US military newspaper Stars and Stripes reported. The US Senate will start confirmation hearing for his replacement, Central Command deputy Marine Lt Gen John Allen from Tuesday.

Meanwhile, the official Voice of America radio quoted US defence officials as saying that President Obama will call for an initial withdrawal of 5,000 troops, followed by an additional 5,000 troops by the end of 2011. About 20,000 additional troops are likely to be withdrawn by the end of 2012.

In his speech on Wednesday night (US time) at the White House, President Obama is also expected to reaffirm the US and Nato commitment to completely transfer security responsibilities to Afghan forces by 2014. The United States currently has about 100,000 troops in Afghanistan, and media reports estimate the US government is spending $10 billion each month fighting the war.

White House spokesman Jay Carney said the president would explain how he would implement the strategy he had outlined for Afghanistan in December 2009, when he approved a “surge” of 30,000 extra troops and promised the first troops would leave in 18 months.

According to a Pew Research poll released on Wednesday, 56 per cent Americans want Mr Obama to remove the troops as quickly as possible. In a CNN/Opinion Research Corporation poll, just more than one in three (36 per cent) people said they favoured the US war in Afghanistan.

But on Wednesday, President Obama received a pledge of support from a political foe, House Speaker John Boehner.

The Republican lawmaker said the plan Mr Obama would announce must be based on the recommendations of military and diplomatic officials on the ground.

“If the president listens to the commanders on the ground and our diplomats in the region and makes a decision, I'll be there to support him. Success in Afghanistan is critically important,” the speaker said.