BEIJING — China delivered a blunt message to North Korea yesterday when it told its leader, Kim Jong Il, that he must refrain from conducting a second nuclear weapons test.

After China’s state-run press suggested for the first time that Beijing might sever North Korea’s oil supplies, a move which could conceivably precipitate the collapse of Mr. Kim’s regime, a senior envoy arrived in Pyongyang to hand down a “personal message” from President Hu of China.

China did not confirm what the message said, but American officials said they believed it to be a strongly worded warning.

The pressure from Mr. Kim’s powerful neighbor appeared to be part of a coordinated international attempt to threaten him to come into line. It came as Secretary of State Rice arrived in the South Korean capital, Seoul, to reinforce America’s own threat that it would seek to toughen sanctions agreed at the United Nations if North Korea went ahead with a second test.

Ms. Rice said negotiations were still possible, but added of the Chinese diplomat’s visit: “I hope [China] has been successful in saying to North Korea that there is really only one path, which is denuclearization and dismantlement of its programs.”

Satellite pictures this week spotted signs of activity around the site of last week’s test, leading to suggestions that a second might be imminent. Mr. Kim has shown no signs of bowing to pressure other than agreeing to the meeting yesterday.

Mr. Kim’s meeting with Tang Jiaxuan, a Chinese lawmaker and former foreign minister, was his first with any representative of the outside world since North Korea conducted its test last week.

That he agreed to meet Mr. Tang could be a sign that he is starting to feel pressure from the international community. He has been known to snub even senior Chinese leaders. “It’s a sign that they are at least engaging,” said one western diplomat.