Israel's prime minister on Tuesday brushed aside suggestions that the threat from Iran's nuclear program has receded, saying he remains convinced that Tehran is "moving forward" with plans for an atomic weapon.

A U.S. intelligence report in December found Tehran had halted its program in 2003. However, Prime Minister Ehud Olmert told reporters that "nothing that we know has changed our attitude on this issue."

"Tell me, why does Iran need enriched uranium at a time when they are supplied by (the) Russians the nuclear fuel for the civilian projects? ... What else do they plan for which they need the most sophisticated ballistic missiles?"

Olmert spoke after meeting with German Chancellor Angela Merkel, whose country has been among those leading efforts to allay concerns over Iran's nuclear ambitions.

Iran — which says its nuclear program is aimed at generating electricity — is under two sets of U.N. Security Council sanctions for refusing to suspend uranium enrichment, a technology that can produce nuclear reactor fuel or material for an atomic bomb.

Last month, the five veto-wielding members of the council — the U.S., Russia, China, Britain and France — along with Germany agreed on a draft resolution for a third round of sanctions.

Merkel has stressed Germany's commitment to the security of the Jewish state in light of Iranian President Mahmoud Ahmadinejad's anti-Israel rhetoric.

Olmert welcomed the "leadership" of Merkel and the British and French leaders in seeking to resolve concerns over Iran and press it to give up uranium enrichment.

"This is mainly the challenge of the big powers; Israel inevitably is ... very interested in these efforts and we will join forces and cooperate with our senior friends in order to help a possible solution that will deter the Iranians from continuing their program," the prime minister added.

A December report by U.S. intelligence agencies concluded that Iran suspended its nuclear weapons program in 2003 and had not resumed it. U.S. officials, however, continue to warn that Iran's enrichment work could easily allow Tehran to resume weapons development.