U.S. Secretary of State John Kerry speaks during a news conference at the London Conference on Afghanistan, in London December 4, 2014. [Photo/Agencies]

Kerry said the London conference was never meant to be a donor meeting for Afghanistan but to hear from Afghan's leaders their vision for the country going forward.

He said donors could be encouraged by the political progress and reforms to come forward later with new aid.

"There will be for sure some effort to increase contributions over time," Kerry said.

But the goal was to make Afghanistan a self-sustaining economy, he said.

Days after becoming president, Ghani signed a new security agreement with the United States, a move his predecessor Hamid Karzai refused to do. The agreement lays out the terms under which US troops may stay in Afghanistan.

"We are committed to ensuring that Afghanistan can never again be used as a safe haven from which terrorists can threaten the international community," Kerry said.

He, however, said Afghanistan would still face security challenges. "Security will grow, it will get better, but no one should be surprised by attacks that will take place here and there," he said.

At the peak of US involvement, there were roughly 100,000 American troops in Afghanistan in 2011.

Beginning next year, about 8,000 American troops, 4,000 other foreign military personnel, are expected to stay on in Afghanistan as part of a NATO-led training and advisor mission. Some 1,800 Americans will conduct counter terrorism mission.