The fresh challenges emerged on the eve of Monday's review conference of the Nuclear Nonproliferation Treaty attended by representatives from some 190 nations. The treaty went into effect 35 years ago with the goal of preventing the spread of nuclear weapons.

But as it meets in New York for the seventh Review Conference since 1970, it faces new worries over Iran and North Korea's nuclear programs, with Pyongyang claiming to have nuclear bombs, and Iran believed to be using its civilian nuclear program to cover up a quest for atomic weapons.

The United States reported that a short-range missile was fired early Sunday from the east coast of North Korea. It flew about 100 kilometersmiles) until it fell into the Sea of Japan.

"It appears that there was a test of a short-range missile by the North Koreans and it landed in the Sea of Japan," White House Chief of Staff Andrew Card told CNN.

Added a US State Department spokesman, Kurtis Cooper: "We have long been concerned about North Korea's missile program and activities and urge North Korea to continue its moratorium on ballistic missile tests."

North Korean shocked the world in August 1998 by firing a long-range missile over Japan that landed in the Pacific Ocean.

Short-range missile launches have been more routine, but have often been timed to send signals.

North Korea's last high-profile launches were in March 2003 when it lobbed two short-range missiles into the Sea of Japan coinciding with the inauguration of South Korean President Roh Moo-Hyun.

On Thursday, US Defense Intelligence Agency director Vice Admiral Lowell Jacoby told US lawmakers that North Korea is believed capable of arming a long-range missile that could reach the United States with a nuclear warhead.

US officials later played down -- but did not deny -- Jacoby's assessment, saying it was not new and theoretical in nature.

The United States has backed six-party talks aimed at ending North Korea's nuclear ambitions, but the talks -- which include the two Koreas, Russia, Japan and the United States -- have stalled since last year.

North Korea kicked out International Atomic Energy Agency inspectors in December 2002 and withdrew from the treaty the following month.

The latest apparent North Korean missile test came as Iran's supreme leader, Ayatollah Ali Khamenei, dismissed Washington's concerns over Tehran's nuclear program.

"The shameless arrogance and rudeness has gone so far that it has given rise to such comments that Iran does not need nuclear technology. This is none of your business," Khamenei said in a televised speech.

His comments came the day after Iran said it was unhappy with the progress of nuclear negotiations with Britain, France and Germany, and warned it may resume uranium conversion activities next week in defiance of a November agreement.

The Europeans, backed by the United States, want Iran to halt all nuclear fuel cycle activities. In return, it is offering a package of trade, security and technology incentives.

Iran has said repeatedly that its enrichment suspension is temporary and voluntary, as it insists on its treaty right to conduct nuclear activities for peaceful purposes.

US Senator John Rockefeller last week urged President George W. Bush to send Secretary of State Condoleezza Rice to the conference, saying her presence would "focus increased international attention on the two most pressing nuclear threats we face as a country: North Korea and Iran."

The Democrat added that the absence of a high-level representative would lead other conference participants to "conclude that the United States is not serious about strengthening the treaty, despite strong statements to the contrary from you and others in your administration."

On Sunday, thousands of demonstrators marched near the UN headquarters in New York, demanding nuclear disarmament. The mayors of Hiroshima and Nagasaki walked at the front of the protest along with survivors of the United States' 1945 nuclear attack on their cities.

Protestors held signs reading: "No more Hiroshimas and Nagasakis" and "Abolish the nuclear weapons."

All rights reserved. � 2005 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse.