The United States will not support a resumption of six-party talks on North Korea’s nuclear disarmament unless the North’s leaders prove they are serious about the effort, Secretary of State Hillary Rodham Clinton said Saturday.

On its own, a private and positive meeting Friday between officials from North Korea and South Korea at a summit of Asian leaders is not enough to restart the talks, Clinton said, adding that North Korea should cease its provocative actions, improve relations with the South and begin dismantling its nuclear program.

“We urge North Korea to demonstrate a change in behavior,” she said in a speech here at Asia’s largest security forum, formally titled the Association of Southeast Asian Nations, or ASEAN.

In meetings with other foreign ministers at the summit, Clinton weighed in on the competing claims to territories in the South China Sea that have led to flare-ups recently between China and its neighbors and criticized Burma for human rights abuses.

Six countries claim portions of the South China Sea, which is believed to hold valuable oil and minerals, but China’s claim is by far the largest, encompassing almost the entire region.

“We also call on all parties to clarify their claims in the South China Sea in terms consistent with customary international law,” Clinton said, proposing that each country base its claims on the location of undisputed lands they already possess, rather than on somewhat arbitrary lines drawn on waters.

The hope is that Clinton’s proposal will force the disputing countries to reevaluate their claims, said a senior State Department official who attended the foreign ministers’ meetings on the issue. All the nations involved have exaggerated claims to some degree, said the official, who was not authorized to speak by name.

The basis of the U.S. argument, however, is the U.N. Law of the Sea Convention, which the United States has not ratified — an irony that others pointed out in private to American officials, the diplomat said.

U.S. officials also used the ASEAN summit to reiterate their demands that Burma’s isolated government release political prisoners and begin a dialogue with its political opposition.

“The country has reached a critical juncture,” Clinton said in one meeting with Asian foreign ministers. The new government, which includes many former military officials who assumed power in a widely criticized election, must differentiate itself from the similarly authoritarian regime of the past, she said.