The Pentagon is considering a buildup of Navy forces in the Persian Gulf as a show of force against Iran, a senior defense official said Tuesday.

Speaking on condition of anonymity because the idea has not been approved, the official said one proposal is to send a second aircraft carrier to the region amid increasing tensions with Iran, blamed for encouraging sectarian violence in neighboring Iraq as well as allegedly pursuing a nuclear weapons program.

The United States and its European allies are seeking sanctions against Iran because of its refusal to stop uranium enrichment, a technology that can be used to produce nuclear fuel for civilian purposes or fuel for a nuclear bomb.

In Tehran, President Mahmoud Ahmadinejad said Tuesday that U.N. sanctions would not stop Iran from pursuing its uranium enrichment program, which he has said is for peaceful development of energy.

Bush administration officials have repeatedly declined to rule out the use of force against Iran, though they have also said their first choice is to rely on diplomacy.

In New York, U.N. Secretary-General Kofi Annan said military action against Iran would be "rather unwise and disastrous." Annan, who is leaving his job Dec. 31, made the comment to reporters at a news conference as the Security Council debated a resolution that would impose sanctions on Tehran.

The idea of building up U.S. Navy forces has been discussed over some time and it's unclear when a decision will be made, the defense official said.

The aircraft carrier USS Dwight D. Eisenhower is already in the region. It left the United States in late September with four other Norfolk-based ships and submarines carrying 6,500 sailors.

The flotilla headed to the Mediterranean Sea and eventually went to relieve the Norfolk-based aircraft carrier USS Enterprise strike group, which was in the region supporting operations in Iraq and Afghanistan.

Also, the U.S. in late October led a naval training exercise aimed at blocking smuggling of nuclear weapons in the Persian Gulf.

The six-nation maneuvers off the coast of Iran were the first of their kind since North Korea's Oct. 9 nuclear test and U.N. sanctions that called on the international community to conduct searches at sea to ensure the reclusive communist nation is not secretly expanding its nuclear program.