WASHINGTON (AP) â€” North Korea's development of a nuclear weapon risks provoking an atomic arms race in East Asia, a senior Republican lawmaker warned Wednesday.

House Foreign Affairs Chairman Ed Royce said South Korea, Japan and Taiwan might seek nuclear weapons if Pyongyang realizes its ambition to miniaturize nuclear warhead it can mount on a missile.

He said this was likely weighing heavily on the mind of China, which was losing patience with its North Korean ally after it ignored warnings not to conduct its latest nuclear test.

The Feb. 12 underground explosion, the North's third, followed a successful long-range rocket launch in December, and drew the stiffest international sanctions yet against the North, with China's support.

Royce said the North's young leader, , was aggressive and had shown "flagrant disregard" for Beijing's counsel, which had caused consternation in China as it weighed the consequences.

"It's clear that the danger of a nuclear arms race in east Asia is very real," Royce told The Associated Press after speaking on Asia policy at the conservative Heritage Foundation think tank.

South Korea, Japan and Taiwan all have civilian nuclear programs but have eschewed weapons development. The United States, which recently announced steps to boost its own missile defense system against the North Korean threat, provides the protection of its nuclear deterrent to both Seoul and Tokyo.

Royce also voiced concern about cooperation between North Korea and Iran, saying they are known to have shared missile technology and that cooperation may extend into the nuclear realm.

"I think everyone suspects it is (going on) and I would be surprised if it were not, given the other transfers that have occurred between North Korea and Iran," he said.

Royce plans to introduce bipartisan legislation in the coming weeks for extra US sanctions along the lines of sanctions applied by the George W. Bush administration against a Macau-based bank holding $25 million in North Korean funds. He said that proved highly effective in 2005 but was lifted prematurely.

He said similar legislation now could cut out of the international banking system and the US market any financial institution that deals in hard currency with the Pyongyang regime.

"That's not a trade-off any financial institution would want to contemplate," Royce said.

Democratic support for such a bill would pressure the Obama administration, which is likely reluctant to apply unilateral sanctions that would alienate China. Beijing is Pyongyang's chief benefactor and has been lax in its implementation of past UN sanctions, but in recent months has taken a tougher diplomatic stance against the North.

Royce, who represents a California district with many Asian-American constituents, is active in Asia policy. The House panel he chairs does not set US foreign policy but can influence it through oversight and legislative actions.

Royce voiced concern Wednesday about rising nationalism in Asia and security threats posed by territorial disputes. He advocated greater US focus on promoting economic prosperity to arrest that trend, and progress on an investment treaty with India and a similar pact with Taiwan.