WASHINGTON: America's top military officer has warned that an Israeli air strike against Iran would make the Middle East more unstable and could add to pressures on the already overworked US forces in the region.

The comments by Michael Mullen, chairman of the Joint Chiefs of Staff, came days after he visited Israel and amid growing international concern that Jerusalem is considering an attack on Iran's nuclear facilities.

"Opening up a third front right now would be extremely stressful for us," Admiral Mullen said, referring to the prospect of a direct clash with Iran while fighting continues in Iraq and Afghanistan.