The United States is raising the pressure on Afghan President Hamid Karzai.

The Obama administration is signaling that a U.S. troop increase in Afghanistan could hinge on a successful runoff election, and that it would be receptive to a power-sharing deal between Karzai and his chief rival.

President Barack Obama and Sen. John Kerry, who pressed the administration's interests while in Kabul, both hinted that pending deliberations on possible troop increases could be affected by the Afghan leader's behavior.

Karzai's weak and corruption-riddled government has been blamed in part for the resurgence of the Taliban and for widespread disillusionment among Afghans. The election in August was marred by massive fraud that led to the discarding of a third of the results. That provided a wedge for the U.S. to press Karzai to agree to the runoff with former Foreign Minister Abdullah Abdullah.

Karzai is widely favored to win the presidential runoff set for Nov. 7.