Japan Warns North Korea on Nuclear Tests

SEOUL, South Korea -- Tensions mounted over North Korea's threat to test its first atomic bomb, with shots ringing out Saturday along the border with South Korea and Japan warning of harsh sanctions if Pyongyang goes nuclear.

With a possible test expected as early as Sunday, the U.N. Security Council issued a stern statement Friday urging the country to abandon its nuclear ambitions and warning of unspecified consequences if the isolated communist regime does not comply.

Jittery nations have warned a test would unravel regional security and possibly trigger an arms race.

A midday incursion Saturday by North Korean troops into the southern side of the no-man's-land separating North and South Korea only stoked the unease.

South Korean soldiers rattled off 40 warning shots at the five communist troops who crossed the center line of the Demilitarized Zone.

It was unclear whether the North Korean advance was intended as a provocation, or was an attempt to go fishing at a nearby stream, an official at South Korea's Joint Chiefs of Staff said on condition of anonymity, citing official policy. No one was hurt, and the North Koreans retreated.

While such border skirmishes are not unheard of, they are relatively rare. Saturday's incursion was only the second this year, the official said.

Meanwhile, world powers were stepping up diplomatic efforts to avert a nuclear test. Japanese Prime Minister Shinzo Abe left for Beijing Sunday for talks with Chinese President Hu Jintao and will then go on to Seoul for talks with South Korean President Roh Moo-hyun the following day.

"North Korea must stop its nuclear tests," Abe demanded as he was leaving for his summits. "I will discuss the situation with leaders of both countries to achieve that goal," he said.

"I want to hold summits to clear the sky for the future of our countries," Abe added.

State Department spokesman Kurtis Cooper said Saturday the United States was concerned about North Korea's threat to test its first atomic bomb and the department was closely monitoring the high tensions.

Also Saturday, South Korea's nuclear envoy announced he will visit Beijing on Monday for two days of talks with Chinese officials about the threatened nuclear test.