CAMP DAVID, Md. - US President Bush and Japanese Prime Minister Shinzo Abe threatened stronger punitive actions against North Korea on Friday if it reneges on a promise to padlock its sole nuclear reactor.

Japanese Prime Minister Shinzo Abe,left, listens as President Bush responds to a reporter's question during their joint news conference,, Friday, April 27, 2007, at Camp David, Md. [AP]

"Our patience is not unlimited," said Bush, standing beside Abe at the Camp David presidential retreat where they stressed the strength of US-Japan relations.

Eager to show that the two nations stand united against Pyongyang, Abe said, "Should the North Koreans fail to keep their promise, we will step up our pressures on North Korea, and on that point again I believe we see eye-to-eye."

In February, North Korea pledged during six-party talks with the United States, Japan, China, Russia and South Korea to shut down its reactor by April 14, a deadline that passed almost two weeks ago.

North Korea says it is waiting to receive some $25 million in funds frozen after Washington blacklisted a Macau bank for alleged complicity in North Korean money laundering and counterfeiting.

Critics of the agreement viewed the US decision to allow the return of the $25 million as evidence Bush was softening his stance against North Korean leader Kim Jong Il to resolve the nuclear standoff.

With Defense Secretary Robert Gates, Secretary of State Condoleezza Rice and Christopher Hill, the lead US negotiator in the North Korea talks, looking on Friday, Bush described his policy on North Korea as "wise," not "soft."

Bush said that if Kim finds another reason to backtrack on his pledge, the US will seek more sanctions against the country. Abe said existing Japanese food and economic sanctions will worsen if North Korea continues to defy the international community.

On another subject, Abe apologized for the Japanese military's actions in forcing so-called "comfort" women to work in military brothels during World War II. He said he had "deep-hearted sympathies" for the women and was sorry for their suffering.

"I, as prime minister of Japan, express my apologies, and also express my apologies for the fact that they were placed in that sort of circumstance," Abe said.

Abe recently created a controversy by suggesting their was no evidence that Japan's Imperial Army had directly coerced Asian women to work in brothels. At Camp David, Abe said he had sought to clarify his remarks in his meetings with members of Congress on Thursday, and again with Bush on Friday.

Bush called it a "regrettable chapter in the history of the world," and said he accepted the prime minister's apology.

Abe said he also talked to Bush about Japanese citizens abducted by North Korea in the 1970s and 1980s. Pyongyang sent home five of the 13 people it admitted having abducted, but insisted the rest were dead.

Japan has demanded proof and says more of its citizens may have been taken. Until the issue is resolved, Tokyo has refused to provide energy and economic aid to North Korea or to normalize relations.

"With regard to the abduction issue, President Bush once again expressed his unvarying commitment to support the government of Japan," Abe said.

Abe's two-day visit to the United States - his first since becoming prime minister in September - was designed to show the depth of US-Japanese relations.

Bush invited Abe to the presidential retreat in Maryland's Catoctin Mountains in part to thank Tokyo for its support in Iraq and Afghanistan. Bush said he hoped Abe could visit his Texas ranch, which the president called his "little slice of heaven."

A brief one-on-one session between the leaders, who decided to be on a first-name basis, turned into a 35 to 40-minute session in the president's private study in Laurel Cabin, according to a senior US official who attended the larger gathering of US and Japanese officials that followed.

During their talks, Bush and Abe agreed to speak with one voice against Iran's nuclear ambitions. They discussed alternative energies, trade, Abe's upcoming visit to the Middle East, climate change and beef.

Citing concerns about mad cow disease, Japan tightly controls US beef imports, allowing cuts only from cattle 20 months old or younger.

"I'm absolutely convinced the Japanese people will be better off when they eat American beef. It's good beef. It's healthy beef," Bush said, adding that he was serving the prime minister an American cheeseburger for lunch.