Three former high-ranking U.S. military officers have called for Britain to help defuse the crisis over Iran's nuclear program, saying military action against Tehran would be a disaster for the region.

In a letter to the Sunday Times newspaper, the three former officers urged President Bush to open talks "without preconditions" with the Iranian government to find a diplomatic solution.

The signatories were retired Lt. Gen. Robert G. Gard, a senior military fellow at the Center for Arms Control and Nonproliferation in Washington; retired Marine Gen. Joseph P. Hoar, former head of U.S. Central Command; and Vice Admiral Jack Shanahan, former director of the Center for Defense Information.

They said Britain "has a vital role to play in securing a renewed diplomatic push" and urged Prime Minister Tony Blair to make it clear he would oppose any military attack on Iran.

The officers said an attack "would have disastrous consequences for security in the region, coalition forces in Iraq and would further exacerbate regional and global tensions."

"The current crisis must be resolved through diplomacy," they said.

The United States and several of its Western allies believe Iran is using its nuclear program as a cover to produce a nuclear weapon — charges Iran denies, saying its aim is to generate electricity. Last week, a respected think tank, the International Institute for Strategic Studies, said Iran was likely two to three years from having the capacity to build a nuclear weapon.

The U.N. Security Council imposed economic sanctions on Iran last month for refusing to halt uranium enrichment, which can be used both for nuclear reactors and to make atomic weapons. The council said it would consider new measures if Iran's defiance continues.

The U.S. government has refused to rule out military action if Iran does not scale back its nuclear activities, and has beefed up the U.S. military presence in the Gulf. Bush also has vowed more aggressive moves against Iranian operatives in Iraq, where the United States accuses Iran of training and arming insurgents who attack U.S. troops.

In a separate letter, Muslim, Jewish and Christian leaders in Britain called for a peaceful resolution to the crisis with Iran.

There is "no justification in international law for attacking Iran militarily and the use of force is not an option at this juncture," said the letter to The Independent on Sunday newspaper, signed by Rabbi Tony Bayfield, head of reform Judaism in Britain; Lord Harries, the former Anglican Bishop of Oxford; and Imam Abduljalil Sajid of the Brighton Islamic Mission.