Pentagon must ready Iran options: top U.S. officer

Admiral Mike Mullen, chairman of the Joint Chiefs of Staff, speaks during a news conference in Kabul December 14, 2009.

WASHINGTON (Reuters) - Diplomacy remains the best course for curbing Iran's nuclear ambitions but the Pentagon must have military options ready should President Barack Obama call for them, the top U.S. military officer said on Monday.

In an annual assessment of the nation's military priorities, the chairman of the Joint Chiefs of Staff, Admiral Mike Mullen, offered no details about what those options might entail but said using force would have limited effect.

"My belief remains that political means are the best tools to attain regional security and that military force will have limited results," Mullen wrote. "However, should the president call for military options, we must have them ready."

Iran appears to be on course to miss the West's year-end deadline for it to accept an enrichment fuel deal aimed at calming international fears about its nuclear program.

If that happens, Washington has made clear that it intends to pursue harsher United Nations sanctions against Iran.

The West fears that the country's nuclear program is aimed at making bombs. Tehran says it seeks only to generate electricity.

Mullen said Obama has given the Iranian leadership "ample incentive to cease developing nuclear arms," adding: "I fully support the effort to focus on diplomatic solutions to existing tensions."

But Mullen played down the chances of a diplomatic breakthrough any time soon, saying: "No resolution is yet in sight."

U.S. Defense Secretary Robert Gates has similarly expressed support for diplomacy, saying military action would only delay the country's nuclear progress temporarily.

Tehran has had years to build underground facilities aimed at hiding and protecting the program in the event of attack from either the United States or Israel, experts say.

(Reporting by Adam Entous; Editing by Vicki Allen)