PHOTO: AFP
Karzai had previously been fiercely opposed to signing a security agreement with Washington which would leave a small contingent of US troops in the country beyond 2014.
US President Barack Obama on Tuesday outlined a plan to withdraw all but 9,800 American troops by the end of the year and pull out the rest by the end of 2016.
The deadline would end more than a decade of military engagement by the US-led forces in Afghanistan that was triggered by the September 11, 2001, attacks on the United States.
"The United States has announced that it will reduce its combat troops and bring the total to a zero," a statement from Karzai's palace said. "The Afghan president is calling on insurgents to use this historic opportunity and end the war."
Afghanistan is due to hold the second round of voting in a presidential election to elect Karzai's successor on June 14 as the incumbent is barred by the constitution by running for office again.
The US plan hinges on Afghanistan's next president signing the Bilateral Security Agreement (BSA) that the United States says it needs in order for troops to stay beyond 2014.
Most analysts expect the deal to be clinched in time, as both candidates in the run-off say they will sign it promptly. The winner is scheduled to take office in August.
In the second round, former anti-Taliban northern alliance leader Abdullah Abdullah will run against Ashraf Ghani, an ex-World Bank economist.
Karzai, whose relationship with the US government soured bitterly during his final term in office, has refused to sign the deal, sending the economy into a downward spiral over concerns about the country's future security.
As part of the post-2014 force, US soldiers are expected to continue training Afghanistan's new 350,000 strong security force and conduct limited counterterrorism operations against al Qaeda and other militants.
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