WASHINGTON — While human rights groups and European officials criticize Pakistan's truce with Taliban fighters, the United States has had little to say.

The muted response Tuesday was a sign — the second in two weeks — of an Obama administration wary about weakening an already fragile government in Islamabad. The U.S. needs that government in the fight against Islamic militants, including the Taliban, that are using Pakistan to stage attacks on U.S.-led forces in Afghanistan.

Pakistan has sent a hard-line cleric to the violent Swat Valley to negotiate with the Taliban. The cleric is pressing militants to give up their arms to honor a pact that imposes Islamic law and suspends a military offensive in Swat and nearby areas. Swat is not far from the semiautonomous tribal regions where al-Qaida and Taliban long have had strongholds.

British and NATO officials have expressed misgivings about a move they said could give extremists a haven in Pakistan.

Secretary of State Hillary Rodham Clinton, however, was cautious when speaking to reporters in Japan. She said Pakistan's efforts still needed to be "thoroughly understood" before she could comment.

"Obviously, we believe that the activity by the extremists in Pakistan poses a direct threat to the government of Pakistan as well as to the security of the United States, Afghanistan and a number of other nations," Clinton said.

The United States relies on nuclear-armed Pakistan to fight resurgent extremists operating along the Afghan-Pakistan border, and is eager to strengthen a Washington-backed government facing economic problems and violence.

The Obama administration is conducting South Asia policy reviews and has appointed Richard Holbrooke as a special envoy for Pakistan and Afghanistan.