The world's nuclear powers are set to face calls to speed up disarmament as a conference on atomic arms control opens in New York.
Protesters call for nuclear powers to disarm
Critics say the US, France, UK, China and Russia have failed to comply with their commitments to disarm.
Iran and North Korea's nuclear activities are also expected to come under scrutiny during a review of the 1970 Nuclear Non-Proliferation Treaty.
On Sunday, thousands of anti-nuclear protesters marched outside the UN.
"Abolish nuclear weapons now!" and "No more Hiroshimas," read banners carried by Japanese demonstrators.
"No nation, no group should test and make material for nuclear weapons. Everything should be banned," said Mayor Tadatoshi Akiba of Hiroshima, the city razed by a US atomic bomb in 1945.
GLOBAL NUCLEAR POWERS
Signed the NPT: US, Russia, UK, France, China
Declared or known: India, Pakistan, Israel
Suspicions over: North Korea, Iran
Formerly had programmes: Algeria, Argentina, Belarus, Brazil, Kazakhstan, Iraq, Libya, Romania, South Africa, Ukraine
Many non-nuclear states want to concentrate on the five original nuclear weapon countries, saying that they had failed to carry out their disarmament commitments.
The non-nuclear nations say they are frustrated with the Bush administration's policies including the rejection of the nuclear test ban treaty, withdrawal from the anti-ballistic missile treaty and the development of new nuclear weapons.
"Achieving nuclear disarmament is not an option, but a legal obligation contained in the NPT," said Mexico's Luis Alfonso de Alba said.
The conference is the seventh review of the Nuclear Non-Proliferation Treaty (NPT), since it came into force 35 years ago.
The review takes place every five years to assess how the treaty can be strengthened and to check how well its 187 signatories are meeting their obligations.
Correspondents say the US and its allies are likely to want the conference to focus on the nuclear activities of Iran and North Korea.
Late last month, Tehran threatened to resume its uranium-enrichment programme and Pyongyang test-fired a short-range missile into the Sea of Japan.
Washington suspects Iran of secretly trying to develop nuclear weapons - a charge Tehran has denied.
Talks between Iranian negotiators and EU counterparts ended in deadlock in London on Friday, but are expected to resume on the sidelines of the meeting.
For its part, North Korea called President George W Bush a "hooligan" and said it did not expect a solution to the stand-off over its nuclear activities during his tenure.
Pyongyang withdrew from the treaty in 2003 and declared that it had the nuclear bomb.
"The conference should condemn North Korea's egregious behaviour," US delegation leader Stephen Rademaker told Congress on Thursday.
But Washington is unlikely to press for tough action against Pyongyang so as to avoid complications in efforts to draw it back to the negotiation table.
The US delegation is expected to call for a ban of "dual use" equipment - which can be used to make both nuclear energy and bombs - from all but the US and a dozen other countries that already have it.
The US and its allies are concerned about the spread of nuclear weapons
Many participants see the open access to the nuclear fuel cycle, and hence bomb fuel, as a loophole in the treaty that needs to be addressed.
The International Atomic Energy Agency (IAEA), the UN's nuclear watchdog, proposes putting fuel production under multi-lateral control by regional or international bodies.
The agency wants its so-called Additional Protocol, which gives it the right to more intrusive short-term inspections, to get universal acceptance.
Currently, less than half of the treaty's signatories have adopted it.
ESTIMATED NUCLEAR WARHEADS, STRATEGIC AND TACTICAL
*The US is also said to have some 3,000 warheads in reserve, while Russia has about 11,000 in non-operational stockpiles
Israel declines to confirm it has nuclear weapons
North Korea claims it has nuclear arms but no details are available
Iran is accused by the US of ambitions to build nuclear arms