US troubleshooter Bill Richardson said Friday he urged North Korean officials on a visit to Pyongyang to exercise "extreme restraint" with South Korea and said he made "a little headway."

The New Mexico governor, a veteran negotiator with the communist state, said he asked North Korea to let the South go ahead with a planned exercise after Pyongyang threatened to strike back with deadly firepower.

"I'm urging them extreme restraint," Richardson told CNN, saying he was "very, very strong with the North Korean foreign ministry officials" during a dinner on Friday.

"I think I made a little headway," Richardson said. "My sense from the North Koreans is that they are trying to find ways to tamp things down."

But Richardson said he was waiting for meetings with senior negotiator Kim Kye-Gwan and a senior North Korean military officer before determining the overall mood in the reclusive state.

"It's a tinderbox. It's very sensitive. So we have to address the immediate concern," he said.

Richardson said he suggested ways to calm the situation, including potentially arranging talks between North and South Korea or working toward the resumption of long-stalled denuclearization talks.

"Let's cool things down. No response -- Let the exercises take place," Richardson said of his message.

"But on all sides I'm urging restraint," Richardson said, describing a warning on Thursday by a senior US general, James Cartwright, as "very encouraging."

Cartwright, the vice chairman of the US Joint Chiefs of Staff, defended ally South Korea's holding of the drills but warned that it could draw a North Korean reaction.

Tensions have soared between the two Koreans in recent months. In November, North Korea killed two marines and two civilians in its first shelling of a civilian area of the South since the 1950-53 Korean War.

Richardson, who served as US ambassador to the United Nations under former president Bill Clinton, has maintained close contacts with North Korea for years. He says he is on a private visit and is not an official envoy.