Washington's recent bid to persuade North Korea to return to nuclear disarmament negotiations included a personal letter to leader Kim Jong Il written by President Barack Obama, a senior U.S. official said.

Envoy Stephen Bosworth took the letter to Pyongyang last week, handing it over to North Korean officials during the Obama administration's first bilateral talks since the U.S. president took office, the official said in Washington.

The official, who spoke Tuesday 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 had responded.

Bosworth did not meet Kim during his three-day trip. But after leaving Pyongyang, he said he conveyed Obama's message 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.

Both Washington and Pyongyang agreed on the need to resume the stalled talks but the North did not make a firm commitment on when it would rejoin the negotiations.

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.

Separately, South Korea's chief nuclear envoy, Wi Sung-lac, plans to leave for Moscow later Wednesday for consultations with Russian officials on North Korea's nuclear program, Foreign Minister Yu Myung-hwan told reporters on Wednesday.

The flurry of trips comes amid a report that Kim is suffering from chronic laryngitis _ probably because of excessive smoking and drinking _ and he can't work without resting every other day.

The illness worsened last month, though the 67-year-old leader has recovered much from last year's reported stroke and a kidney disease, said the Seoul-based Open Radio for North Korea, a radio station specializing in North Korean news.

The station cited an unidentified "high-level source" in the North. South Korean officials could not confirm the report.

Kim's health has security implications beyond the Korean peninsula because of fears of a possible power struggle if he were to die without naming a successor, a scenario that could affect the North's nuclear programs and the disarmament process.