Japan's foreign Minister Katsuya Okada on Monday told Iran's top nuclear negotiator Saeed Jalili that Iran's current nuclear standoff is "regrettable," and of " great concern," according to ministry officials.

Okada, at a press conference in Tokyo on Monday, described the ensuing debate that erupted between Iran and the United Nations, following the UN's proposal for Iran to transfer low-enriched uranium out of Iran to be converted as fuel for a medical research reactor, as "extremely regrettable."

Jalili maintained that Iran has granted full access of the International Atomic Energy Agency (IAEA) to inspect its nuclear facilities and that no evidence has emerged that Iran's nuclear program is being used for anything other than generating energy and thus Tehran is opposed to the IAEA's proposal.

Jalili insisted on Monday that his country's nuclear program is for civilian purposes only and called for the disarmament of all nations with atomic weapons, adding that all countries have the right to develop nuclear energy.

Jalili, whose five-day trip to Japan also includes a visit to the western Japanese city of Hiroshima, which suffered an atomic bombing during World War II, came amid increased tension between Tehran, the UN and the U.S., who suspect Iran plans to enrich uranium at a grade high enough to be used for nuclear weapons.

"I hope you will see how a nuclear weapon can bring about a tragic outcome," Okada said to Jalili, referring to his planned visit to Hiroshima.

"The crime that was committed in Hiroshima must never be repeated," Jalili said to reporters in response.

The U.S. has given Iran until the end of the year to accept the proposal for its uranium enrichment program, warning that further action will be taken should the country, already under heavy sanctions, opt not to comply.

Adding to concerns about Iran's nuclear program was the test firing of an upgraded version of its most powerful missile on Dec. 16.

The new missile, a solid-fuel remodel of the two-stage Sejil-2, is more accurate than its previous liquid-fuel rockets, according to an IAEA spokesperson.

The missile test demonstrated Iran is now easily capable of striking any part of Israel, which Iranian President, Mahmoud Ahmadinejad, said four years ago should be "wiped off the map."

Analysts said the test appeared aimed at dissuading Israel from launching a pre-emptive military attack on any of Iran's nuclear facilities, which Western powers believe house Iran's secret nuclear weapons development program.

The new medium-range missile tested by Iran is "not particularly different than what we've seen in the past," said Pentagon defense spokesman Geoff Morrell, following the launch.

Washington has condemned the launch saying that the experiment undermines Teheran's insistence of peaceful intentions, and will be looked upon seriously by the world.