SEOUL: North Korea told a senior U.S. envoy that U.N. sanctions imposed on the communist regime for its nuclear defiance must be lifted, a report said Wednesday.

North Korean officials conveyed the message to Stephen Bosworth, President Barack Obama's envoy on North Korea, during the diplomat's trip to Pyongyang last week for high-level talks, South Korea's Yonhap news agency reported, citing an unidentified diplomatic source.

South Korean officials in charge of nuclear negotiations were not immediately available for comment.

Bosworth went to North Korea to try persuading the regime to return to disarmament talks also involving South Korea, Russia, China and Japan. The closely watched talks were the Obama administration's first with Pyongyang since the U.S. president took office in January.

Bosworth said North Korea agreed on the need to resume the talks but did not make a firm commitment on when it would rejoin the negotiations.

The process had yielded pacts promising North Korea much-needed aid and other concessions in return for step-by-step disarmament. However, Pyongyang walked away from the talks this year in anger over U.N. Security Council condemnation of a rocket launch widely seen as a test of its long-range missile technology.

The U.N. Security Council tightened sanctions in June after North Korea conducted an underground nuclear test, its second, in defiance of an earlier ban. The sanctions, aimed at derailing North Korea's nuclear weapons program, ban the country from developing its nuclear program and selling conventional arms.

During his three-day visit, Bosworth did not meet with North Korean leader Kim Jong Il. However, he relayed a personal letter from Obama to the reclusive Kim, a senior State Department official said Tuesday in Washington.

The official, who spoke on condition of anonymity because of the sensitive nature of the diplomacy, would not describe the contents of the letter but said they fit with Bosworth's general message.

"The North Koreans have a choice: continued and further isolation or benefits for returning to the six-party talks and dismantling their nuclear weapons program," the official said. The official was not aware whether Kim has responded.

Bosworth said last week that Obama made clear that the United States is ready to work with its allies to offer North Korea "a different future" if Pyongyang chooses to rejoin the disarmament talks and take irreversible steps toward dismantling its atomic program.

Amid a flurry of disarmament diplomacy, Chinese Vice President Xi Jinping was scheduled to visit South Korea later Wednesday for talks with President Lee Myung-bak and other South Korean officials. Xi and Lee are expected to discuss North Korea on Thursday.

The North's reported demand comes as Thai authorities are inspecting 35 tons of weapons seized from a cargo plane loaded in North Korea — the latest known case of Pyongyang's illicit weapons trade in violation of U.N. sanctions.

Thai officials impounded the Ilyushin IL-76 transport plane Saturday after authorities discovered explosives, rocket-propelled grenades and components for surface-to-air missiles.

North Korea is believed to earn hundreds of millions of dollars every year by selling missiles, missile parts and other weapons to countries such as Iran, Syria and Myanmar.