President Barack Obama has nominated General Joseph Dunford, the deputy Marine commander, to lead the war effort in Afghanistan and oversee plans to withdraw most of the US combat forces from the country by the end of 2014.
Dunford, if confirmed by the Senate, would replace General John Allen, who was nominated by the president on Wednesday to become NATO's supreme allied commander for Europe.
Dunford, who served in Iraq, has been assistant commandant of the Marine Corps since October 2010 and had been widely expected to take charge of US and NATO troops in Afghanistan as Allen rotated out of the post.
"If confirmed by the Senate, he will lead our forces through key milestones in our effort that will allow us to bring the war to a close responsibly as Afghanistan takes full responsibility for its security," Obama said in a statement.
Dunford would assume command of 68,000 US troops who make up the bulk of the coalition force of about 100,000.
Allen, nominated to succeed Admiral James Stavridis in a post traditionally held by a US officer, led the NATO campaign in Afghanistan from July 2011.
Both nominations by Obama are subject to US Senate confirmation. If approved, the moves would take place in early 2013.
'Served with distinction'
"For more than a year, General Allen has served with distinction as the commander of US forces and NATO's International Security Assistance Force [ISAF] in Afghanistan, seeing us through a critical period in our military efforts and in Afghanistan's transition," Obama said in a statement.
"Under General Allen's command, we have made important progress towards our core goal of defeating al-Qaeda and ensuring they can never return to a sovereign Afghanistan."
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Allen commanded a coalition force from 50 different countries, giving him the experience to deal with the often sensitive and conflicting wishes of NATO's 28 member states and 22 partners.
Dunford would become the fifth top allied commander in Afghanistan in a five year period.
Meanwhile, the UN defended on Wednesday its recommendation that the 15-member UN Security Council postpone a planned visit to Afghanistan this month over security concerns after some diplomats questioned the UN threat assessment.
Diplomats said the decision to postpone the trip came after UN security chief Gregory Starr recommended earlier this month that they not travel to Afghanistan in the coming weeks, citing concerns for the safety of council diplomats.
Some council diplomats privately questioned the UN recommendation as vague, but others told Reuters news agency that it would be unwise to question Starr's assessment of the risk level in Afghanistan.
UN spokesman Farhan Haq said a security assessment had been made to the council based on the best information
"We stand by the recommendation, but will not comment further," he said.