U.S. Secretary of State Hillary Clinton, at a news conference in Phuket, warns North Korea faces 'unrelenting pressure' to disarm its nuclear weapons program. (Apichart Weerawong/Associated Press)

The U.S. could beef up the military capacity of its Persian Gulf allies if Iran continues to develop its military program, U.S. Secretary of State Hillary Clinton said.

Clinton, in Thailand for a two-day security conference to discuss North Korea and a range of other regional issues with her Asian counterparts, also warned North Korea that it faces further isolation over its nuclear program.

Clinton, who appeared Wednesday morning on a Thai TV talk show in Bangkok, addressed Iran's nuclear program. She cautioned the U.S will take "crippling action" to upgrade the defence of their allies in the Persian Gulf region if Tehran gets a nuclear bomb.

"We want Iran to calculate what I think is a fair assessment: that if the United States extends a defence umbrella over the region, if we do even more to develop the military capacity of those [allies] in the Gulf, it is 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," Clinton said.

'I think that's a mistake'

But Dan Meridor, Israel's minister of Intelligence and Atomic Energy, told Army Radio that Clinton's statement suggests the U.S believes a nuclear Iran is a done deal.

"I was not thrilled to hear the American statement from yesterday that they will protect their allies with a nuclear umbrella, as if they have already come to terms with a nuclear Iran. I think that's a mistake," he said.

Later, at a news conference in Phuket, Clinton said North Korea would face "the unrelenting pressure" of international sanctions if it did not end its nuclear weapons program.

"We have made it very clear to the North Koreans that if they will agree to irreversible denuclearization that the United States, as well as our partners, will move forward on a package of incentive and opportunities — including normalizing relations — that will give the people of North Korea a better future."

Clinton said China, Japan, Russia and South Korea agree with Washington on the core goal of irreversibly ending North Korea's nuclear program.

"We do not want to be in another negotiation that doesn't move us toward the goal of denuclearization," she said. "So we want verifiable, irreversible steps taken."

With files from The Associated Press