Iran's "pursuit of nuclear weapons will not advance its security"
Iran and North Korea will face severe consequences if they do not abandon their nuclear ambitions, US Secretary of State Hillary Clinton has warned.
At a regional summit in Thailand, Mrs Clinton said the US was prepared to bolster the defence of Gulf allies if Iran developed nuclear weapons.
A US Gulf "defence umbrella" would make it unlikely Iran would be stronger or safer with a weapon, Mrs Clinton said.
She said North Korea must irreversibly denuclearise before returning to talks.
Six-party talks involving the North, the US, South Korea, China, Japan and Russia have stalled over Pyongyang's continued efforts to enhance its nuclear programme.
"We have made it very clear to the North Koreans that if they will agree to irreversible denuclearisation, the United States as well as our partners will move forward on a package of incentives and opportunities including normalising relations," she told a news conference in the Thai resort of Phuket.
"We do not want to be in another negotiation that doesn't move us toward the goal of denuclearisation," she said.
"So we want verifiable, irreversible steps taken."
Addressing the day's theme, of nuclear proliferation, Mrs Clinton said that Iran faced the prospect of sparking an arms race in its region if it pursued nuclear weapons.
"It may render Iran less secure, not more secure," she said.
Earlier, Mrs Clinton said the US was still offering engagement to Iran but warned that the "nuclear clock was ticking".
Foreign ministers from the Association of South East Asian Nations (Asean), as well as EU and US envoys, met on Wednesday in Thailand.
Asean leaders are meeting for their regional conference in Thailand
Mrs Clinton reiterated President Barack Obama's policy that talks were still an option between Iran and the US, but that "crippling action" could also be considered.
Speaking in an interview for Thai television, she said: "If the US extends a defence umbrella over the region, if we do even more to support the military capacity of those in the Gulf, it's unlikely that Iran will be any stronger or safer because they won't be able to intimidate and dominate as they apparently believe they can once they have a nuclear weapon."
Western powers fear that Iran is developing nuclear weapons, but it says its nuclear development is based entirely on enriching uranium to the level needed for power.
Iran has not responded to Mr Obama's offer of engagement.
However, one Israeli government minister, Dan Meridor, said Mrs Clinton's words signalled that the US was becoming resigned to the idea that Iran will one day develop atomic weapons.
"This is a mistake," said Mr Meridor. "I think it would be more appropriate not to accept the premise that Iran has turned nuclear but to try to prevent this."
In Thailand, Mrs Clinton also spoke about concerns over the transfer of nuclear technology from North Korea to Burma.
Asean has a policy of non-interference in members' affairs, but Burma has provoked widespread censure.
Mrs Clinton condemned Burma's treatment of jailed pro-democracy leader Aung San Suu Kyi, saying Asean could consider expelling Burma from the regional grouping.
"It would be an appropriate policy change to consider," she said when asked about the possibility on Thai television, AFP reported.
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