WASHINGTON — The Obama administration confronted two of its most intractable foreign policy issues Monday, seeking ways to contain rising tensions with nuclear-armed North Korea and, separately, pressing Iran to halt a uranium-enrichment program suspected of being part of a secret nuclear weapons program.

Secretary of State Hillary Rodham Clinton agreed with her South Korean and Japanese counterparts at a meeting in Washington not to resume long-stalled nuclear negotiations with North Korea until its Stalinist regime ends “provocative and belligerent behavior.”

In Geneva, a top U.S. diplomat joined representatives of the European Union, Britain, France, Germany, Russia and China for their first talks with Iran in more than a year.

The Korean crisis and Iran’s defiance of United Nations demands to suspend uranium enrichment represent the most serious challenges facing President Obama’s effort to curb the global spread of nuclear weapons.

In Washington, the Pentagon announced that Adm. Mike Mullen, the chairman of the Joint Chiefs of Staff, would depart Monday for South Korea to reiterate U.S. military support for Seoul. He then is to visit Japan.

Clinton said that she, Japanese Foreign Minister Seiji Maehara and his South Korean counterpart, Kim Sung-hwan, agreed not to resume talks with North Korea on ending its nuclear program in exchange for aid and other benefits until it ended behavior that “jeopardizes peace and stability in Asia.”

“They need to demonstrate a seriousness of purpose in ending their provocations and let the world know they are now ready to come to the table and fulfill the commitments they have already made,” Clinton told a news conference.

In Geneva, Iran agreed to discuss international concerns that it’s enriching uranium for weapons, contrary to earlier assertions by senior Iranian officials that the program wasn’t open for discussion.

Iranian negotiator Saeed Jalili said Iran “wanted to allay the fears of the international community,” said a Western official close to the talks, an account that other officials confirmed.

The officials requested anonymity because they weren’t authorized to speak publicly.

Jalili also brought up bomb attacks last week in Tehran on two nuclear scientists, one of whom died, saying “people have made a connection between the attacks and the talks,” the Western official said.

Jalili did not, however, repeat Iranian accusations of Western involvement in the attacks.

In a negative sign, officials said that the U.S. representative, Undersecretary of State William Burns, failed to meet one-on-one with Jalili. The pair met at the last so-called “P5 Plus One” session with Iran in October 2009.

The U.S., European, Chinese and Russian representatives all stressed the “lack of trust” in Iran and the “importance of transparency” in assuaging concerns that the Islamic Republic is hiding work on nuclear arms, the officials said.

The representatives also reiterated an earlier confidence-building proposal for Iran to ship its stocks of low-enriched uranium to a third country to prove that they won’t be purified into weapons-grade highly enriched uranium.

Iran, which hid its enrichment program from U.N. inspectors for 18 years, says it’s intended only to produce low-enriched uranium fuel for power plants. Tehran rejects as fakes documents acquired by the U.N. International Atomic Energy Agency showing that it was researching arming missiles with nuclear warheads.

Iran has been hit with four rounds of U.N. sanctions and unilateral measures by the U.S. and EU, and U.S. officials said that it agreed to revive the talks after a 14-month hiatus because of the economic pain it’s feeling.