The United States is warning Afghanistan to “step up” security or put the smooth withdrawal of U.S. forces at risk.

Outgoing U.S. Defense Secretary Robert Gates delivered the stern message to Afghan President Hamid Karzai during a visit to Kabul Saturday.

He also told reporters during a news conference that while the international community will support Afghanistan, the military commitment to Afghanistan is “not infinite in either time or resources.”

Gates' 12th and final trip to Afghanistan comes as tensions over continuing civilian casualties in Afghanistan have further strained U.S.-Afghan relations.

President Karzai expressed outrage earlier this week at civilian casualties following an airstrike on a private home. On Saturday, he again demanded an end to the strikes saying Afghans “cannot take this anymore.”

Before arriving in Afghanistan, the U.S. defense secretary acknowledged that both U.S. and Afghan civilians have grown weary of war. But he also said any failure to complete the mission would be “the most costly thing of all.”

Before leaving Afghanistan, Gates is scheduled to meet with U.S. troops.

It has been nearly 10 years since U.S.-led forces invaded Afghanistan to topple the Taliban government and go after al-Qaida leader Osama bin Laden.

U.S. special forces killed bin Laden last month during a raid in neighboring Pakistan. In the meantime, the U.S.-Afghan relationship has become more tense, with President Karzai repeatedly criticizing the U.S. and NATO for killing civilians.

The U.S. has set next month as the start date for withdrawing troops from Afghanistan. U.S. and NATO forces are scheduled to transfer security responsibilities to Afghan forces by the end of 2014.

Defense Secretary Gates told the news conference in Kabul it would premature to make any big changes to the U.S. strategy, adding there would be “no rush to the exits.”

He also said it would take some more time to assess what the death of terror mastermind Osama bin Laden means for the fight against the Taliban.

Earlier Saturday, at a security conference in Singapore, the outgoing U.S. defense secretary said there could be peace talks with the Taliban within a year. Gates said the talks would be a result of NATO's ground advances in Afghanistan that have put pressure on the insurgents.

The defense secretary said if the international coalition can sustain its successes, then the possibility of political talks and reconciliation might be “substantive enough” to offer some “hope of progress.”

However, Secretary Gates stressed the Taliban will have to cut ties with al-Qaida and surrender all arms if it is to have any role in the future of Afghanistan.