TEHRAN (Fars News Agency) -- Three former senior US military officials warn that any military action against Iran would have "disastrous consequences" and urged Washington to hold immediate and unconditional talks with Tehran.

The Bush administration has increased the regularity and vehemence of its accusations against Iran, prompting speculation it could be laying the ground for military attack against the Islamic state, Reuters reported.

In a letter to London's Sunday Times newspaper, the three former US military leaders said attacking Iran "would have disastrous consequences for security in the region, coalition forces in Iraq and would further exacerbate regional and global tensions," they wrote.

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

The letter was signed by retired Army Lt. Gen. Robert Gard, a former military assistant to Defense Secretary Robert McNamara, retired US Marine Corps Gen. Joseph Hoar, a former commander in chief of US Central Command; and retired Navy Vice Adm. Jack Shanahan, a former director of the Center for Defense Information.

They urged the US government to "engage immediately in direct talks with the government of Iran without preconditions.

"There is time available to talk, we must ensure that we use it," they said.

The three men have joined previous petitions calling on the Bush administration to change course in its policy on Iran.

Washington broke ties with Iran in 1980. It has offered to hold direct talks with Iran but only once Tehran halts its drive to produce nuclear fuel through uranium enrichment.

Iran, which says it wants to enrich uranium to make nuclear reactor fuel, has refused.

US Defense Secretary Robert Gates on Friday said Washington was not planning for war with Iran.