Iran denounced the United States on Monday for contemplating possible nuclear strikes against Iranian targets and urged the United Nations to take urgent action against what it called a dangerous violation of international law.

In a letter to U.N. Secretary-General Kofi Annan obtained by The Associated Press, Iran's U.N. Ambassador Javad Zarif called President George W. Bush's refusal two weeks ago to rule out a U.S. nuclear strike on Iran and a similar follow-up statement by Secretary of State Condoleezza Rice "illegal and insolent threats."

Bush was asked on April 18 whether U.S. options regarding Iran "include the possibility of a nuclear strike" if Tehran refuses to halt uranium enrichment. "All options are on the table," the president replied, but he stressed that the United States will continue to focus on diplomacy.

Iran insists it is legally entitled under the Nuclear Nonproliferation Treaty to enrich uranium to provide fuel for civilian power plants but the United States suspects its real aim is to produce nuclear weapons, a view backed by Britain and France.

Zarif said the use of "false pretexts" by senior U.S. officials "to make public and illegal threats of resort to force against the Islamic Republic of Iran is continuing unabated in total contempt of international law and fundamental principles of the United Nations Charter."

The "U.S. aggressive policy" of contemplating the possible use of nuclear weapons also violates the Nuclear Nonproliferation Treaty and other U.S. multilateral agreements, he said.

"Such dangerous statements, particularly those of the United States president, widely considered in political and media circles as a tacit confirmation of the shocking news on the administration's possible contemplation of nuclear strikes against certain targets in Iran, defiantly articulate the United States policies and intentions on the resort to nuclear weapons," Zarif said.

"In view of the past illegal behavior of the United States, these assertions yet again constitute matters of extreme gravity that require an urgent, concerted and resolute response on the part of the United Nations and particularly the Security Council," he said.

"It is indeed regrettable that past failures of the United Nations in responding to these illegal and inexcusable threats have emboldened senior United States officials to go further and even consider the use of nuclear weapons as an `option on the table'," the Iranian ambassador added.

After lengthy negotiations, the U.N. Security Council adopted a statement a month ago demanding that Iran stop enriching uranium. A new report Friday from the International Atomic Energy Agency, the U.N. nuclear watchdog, confirmed what the world already knew: Iran has refused to stop enriching uranium.

The United States, Britain and France immediately announced plans to introduce a new Security Council resolution this week which would make Iran's compliance with their demands mandatory. To intensify pressure, they want the resolution under Chapter 7 of the U.N. Charter which means it can be enforced through sanctions or military action.

China and Russia, the two other council members with veto power, oppose sanctions and military action and want the Iran nuclear issue resolved diplomatically, with the IAEA taking the lead, not the Security Council.

U.N. spokesman Stephane Dujarric said Annan had not yet received the letter. The U.S. Mission to the United Nations said it was also waiting to see the letter before commenting.