U.S. Secretary of State Hillary Clinton arrived in Kabul on Wednesday night for an unannounced visit as helicopters hovered in the sky of the Afghan capital to beef up security.

Clinton will meet Afghan president Hamid Karzai on Thursday to seek a political solution to the ten-year-old conflict with the Taliban militant group.

Afghan government's reconciliation effort suffered setback with the assassination of top Afghan peace negotiator Burhanuddin Rabbani in a suicide bomb attack at his home in Kabul last month.

While the U.S. offered peace talks with Taliban, whose regime was toppled by the U.S.-led invasion in late 2001, the insurgent group insists on the precondition that the foreign troops leave Afghanistan.

The U.S. will withdraw 33,000 troops by the end of summer in 2012 and will complete security transfer from U.S.-led coalition force to Afghan national army by 2014.

Also on the table for Hillary Clinton to consult with President Karzai is the long-term strategic framework pact between the United States and Afghanistan, which is hoped by the U.S. side to be signed as early as this year.