China gave the International Atomic Energy Agency intelligence about Iran's nuclear program despite Beijing's opposition to harsh U.N. Security Council sanctions on Tehran, according to diplomats familiar with the matter.

China and Russia have acted as a brake within the Security Council, consistently watering down a U.S.-led push to impose severe penalties on Tehran. A Chinese decision to provide information for a probe into Iran's alleged nuclear weapons program could be a sign of growing international unease about the Islamic republic's denials that it never tried to make nuclear weapons.

The new development was revealed to The Associated Press by two senior diplomats who closely follow the IAEA probe of Iran's nuclear program.

The IAEA declined comment and no one answered the phone Wednesday at either the Chinese or Iranian missions to the IAEA.

The diplomats - who requested anonymity because their information was confidential - said China was the most surprising of a substantial list of nations that have recently forwarded information that could be relevant in attempts to probe past or present nuclear weapons research by Iran.

State Department spokesman Sean McCormack told reporters Wednesday that he could not confirm that China had provided information on Iran.

"We've worked very well with China on the issue overall," McCormack said.

John Bolton, who has served as U.S. ambassador to the United Nations and U.S. undersecretary of state in charge of the Iran nuclear dossier, said any such Chinese move would be "potentially significant" because of Beijing's former military ties to Tehran.

"We have known or felt for some time that both in the ballistic missile field and in the nuclear field there has been cooperation for some time," he said in a interview. "The Chinese have systematically denied cooperation in the nuclear field."

The diplomats who revealed the Chinese cooperation said the U.N. nuclear watchdog had started getting more information from member nations after a February presentation by the agency to its 35 board members summarizing the intelligence on Iran's alleged clandestine nuclear arms program.

Iran said last month that any information suggesting it ever had a nuclear arms program was fabricated and the issue was closed.

In the first test of whether Iran will truly stonewall the IAEA in its attempt to probe the alleged military programs, director general Olli Heinonen plans to meet in coming days with Ali-Ashgar Soltanieh, Iran's chief delegate to the agency, to press for answers, diplomats said.

Suspected weapons-related work outlined in the February presentation and IAEA reports preceding it include:

- Uranium conversion linked to high explosives testing and designs of a missile re-entry vehicle, all apparently interconnected through involvement of officials and institutions.

- Procurement of so-called "dual use" equipment and experiments that also could be used in both civilian and military nuclear programs.

- Iran's possession of a 15-page document outlining how to form uranium metal into the shape of a warhead.