U.S. Defense Secretary Leon Panetta and Afghan President Hamid Karzai discussed on Thursday, January 10 the "last chapter" in building a sovereign Afghanistan that can provide its own security, including the nature of U.S. involvement after combat troops withdraw in 2014, Reuters said.

Panetta said he and Karzai made "very good progress" on the issues they discussed, but he declined to say whether they had agreed on the size of any residual U.S. force that would remain in Afghanistan to do counterterrorism operations and training once combat troops withdraw.

Panetta said both sides were committed to the goals approved at the NATO summit in Chicago in May, which calls for a continuing effort by members of the alliance to train, advise and assist Afghan forces. Karzai is scheduled to meet President Barack Obama on Friday for more talks on the remaining issues.

The Obama administration has been considering a residual force of between 3,000 and 9,000 troops in Afghanistan to conduct counterterrorism operations while providing training and assistance for Afghan forces. But the administration said this week it did not rule out a complete withdrawal after 2014.

While Karzai has been critical of U.S. troop activity in Afghanistan, it is unclear how Afghan forces would perform without U.S. helicopters, medical facilities, intelligence and other military support, of which Afghanistan has very little.