YEONPYEONG ISLAND, South Korea -- South Korean President Lee Myung-bak gathered his national security leaders for strategic talks Tuesday as troops braced for possible North Korean retaliation a day after conducting artillery drills on an island the North bombed last month.

North Korea has so far backed off threats to strike the South again for conducting live-fire military drills on Yeonpyeong Island. Similar drills last month triggered a North Korean artillery attack that killed four South Koreans, including two civilians.

Still, South Korea's military said it was prepared for any unexpected North Korean provocation.

"We will mobilize reconnaissance and surveillance assets of South Korea and the U.S. combined force and intensively monitor North Korea's military activities," Defense Minister Kim Kwan-jin told lawmakers before leaving for the security meeting.

Meanwhile, New Mexico Gov. Bill Richardson praised North Korea's "statesmanlike" restraint as he wrapped up a four-day trip to North Korea.

Richardson, a former U.S. ambassador to the United Nations who has served as an unofficial envoy to North Korea in the past, told Associated Press Television News in Pyongyang that his trip yielded "positive" results.

"It was a good visit -- positive results in our discussions with North Korea," he said Tuesday morning before boarding a plane in Pyongyang.

Richardson said the North agreed to let U.N. atomic inspectors visit its main nuclear complex to make sure North Korea is not producing enriched uranium for a nuclear bomb, according to a statement from his office.

The United States, however, indicated skepticism that North Korea would do anything more than talk.

"North Korea talks a great game. They always do," U.S. State Department spokesman P.J. Crowley said in Washington. "The real issue is what will they do. If they are agreeable to returning IAEA (International Atomic Energy Agency) inspectors to their country, they need to tell the IAEA that."

The North expelled U.N. inspectors last year, and last month showed a visiting American scientist a new, highly advanced uranium enrichment facility that could give it a second way to make atomic bombs, in addition to its plutonium program. Richardson also said that Pyongyang was willing to sell fresh fuel rods, potentially to South Korea.

"This is the way countries are supposed to act," Crowley told reporters. "The South Korean exercise was defensive in nature. The North Koreans were notified in advance. There was no basis for a belligerent response."

The North's apparent conciliatory gestures came after South Korea launched fighter jets, evacuated hundreds of residents near its tense land border with the North and sent residents of islands near disputed waters into underground bunkers in case Pyongyang followed through on a vow to attack over the drills.

"We have to show North Korea that we are committed to respond to any kind of North Korean provocation," a senior South Korean government official said Tuesday.

He said the lack of response Monday did not mean Pyongyang was backing down, noting that North Korea thrives on "surprise" attacks and that South Korean military was braced for possible provocations in coming days. The official spoke on condition of anonymity, citing the sensitivity of the matter.

North Korea has previously been accused of using a mix of aggression and conciliatory gestures to force international negotiations that usually net it much-needed aid. Real progress on efforts to rid the North of its nuclear weapons programs has been rare.

On Nov. 23, the North shelled Yeonpyeong Island, a tiny enclave of fishing communities and military bases about 7 miles (11 kilometers) from North Korean shores in response to an earlier round of South Korean live-fire maneuvers.

The artillery barrage killed two marines and two construction workers and was the first attack targeting civilian areas since the 1950-53 Korean War.

The Korean peninsula, still technically in a state of war, has remained tense for weeks, and U.N. diplomats holding an emergency meeting in New York on Sunday failed to find a solution to the crisis.

Pyongyang is believed to be seeking one-on-one talks with Washington before returning to stalled nuclear disarmament negotiations hosted by China. The U.S. and South Korea, however, say resuming the talks without requiring meaningful movement on past nuclear commitments would reward North Korea for bad behavior.

China has urged a resumption of the talks, and diplomats said Beijing successfully prevented Sunday's U.N. Security Council meeting from issuing a statement condemning the North's shelling -- as the U.S. and others had wanted.

China's deputy U.N. ambassador Wang Min urged both sides "to exercise maximum restraint," avoid increasing tensions and solve differences through peaceful dialogue and engagement.

"China will continue to make every efforts towards this end," he said Monday. "Calm rather than tensions, dialogue rather than confrontation, peace than warfare -- this is the strong aspiration and voice of the peoples from both sides of the peninsula and the international community."

Diplomats at the U.N. blamed China for refusing to condemn North Korea for two deadly attacks this year that helped send relations to their lowest point in decades.

China is the North's most important ally and has come under pressure to leverage its influence to rein in the North in the wake of the attack.

Beijing, which provides crucial food and fuel aid to Pyongyang, is wary of pressuring the North in a way that could destabilize it, fearing in part a government collapse and a flood of refugees into northeastern China.

It was unclear if China persuaded North Korea not to react to Monday's drills.

Richardson appeared to suggest that his visit contributed to the North's backing down.

"During my meetings in Pyongyang, I repeatedly pressed North Korea not to retaliate. The result is that South Korea was able to flex its muscles, and North Korea reacted in a statesmanlike manner," Richardson said in a statement. "I hope this will signal a new chapter and a round of dialogue to lessen tension on the Korean peninsula."

North Korea called Monday's drills a "reckless military provocation" but said they held fire because Seoul had changed its firing zones.

The official Korean Central News Agency carried a military statement that suggested the North viewed Monday's drills differently from those that provoked it last month because South Korean shells landed farther south of the North's shores.

The North claims the waters around Yeonpyeong as its territory. Several bloody naval skirmishes have occurred in recent years along the Koreas' disputed western sea border, which the North does not recognize.