North Korea threatened South Korean passenger planes flying near its airspace on Thursday and accused the U.S. and South Korea of attempting to provoke a nuclear war with upcoming joint military drills.

In response, South Korea's Korean Air and Asiana Airlines rerouted their flights to stay clear of North Korean airspace, the Yonhap news agency reported.

The threat from North Korea's Committee for the Peaceful Reunification of the Fatherland comes four days before annual U.S.-South Korean exercises are to begin across South Korea and amid concerns the North is preparing to test-fire a long-range ballistic missile.

The North is "compelled to declare that security cannot be guaranteed for South Korean civil airplanes flying through the territorial air of our side and its vicinity ... while the military exercises are under way," the committee said in statement carried by the state-run Korean Central News Agency.

It did not say what kind of danger South Korean planes would face or whether the threat means the North would shoot down planes. It was also unclear whether the statement was a warning to clear the air before a possible missile launch.

Analysts said there is little chance North Korea would shoot down planes because it knows such a move would lead to a full-scale war, and said the threat was aimed at escalating tensions.

The North is "exercising all its brinksmanship," said Kim Sung-han, an international relations professor at Seoul's Korea University. "I would say it's just rhetoric for now."

South Koreans, however, still vividly remember a North Korean bomb that exploded on a Korean Air flight in 1987, killing all 115 people on board, and another Korean Air jet that was shot down by a Soviet fighter jet in 1983, killing all 269 people aboard.

North Korea has railed for days against the U.S.-South Korean military drills at a time of mounting tensions on the Korean peninsula.

The North called a meeting with generals from the U.S.-led U.N. Command inside the Demilitarized Zone on Monday — the first general-level talks between the two sides in nearly seven years — and reportedly demanded that Washington call off the exercises.

The U.S. military said it would go ahead with the drills involving 26,000 U.S. troops, an unspecified number of South Korean soldiers and a U.S. aircraft carrier. Both Washington and Seoul insist the annual exercises are purely defensive, not preparations for an invasion as the North claims.

High-ranking U.N. and North Korean officials were scheduled to meet again at the DMZ on Friday.

Stepping up the rhetoric ahead of the second meeting, North Korea said the drills would constitute a "criminal act against peace" and were "aimed at bringing the dark clouds of a nuclear war to hang over the Korean peninsula."

North Korea announced last week that it is preparing to send a communications satellite into space but regional powers suspect the claim is a cover for the launch of a long-range missile capable of reaching Alaska.

Analysts say satellite images show brisk activity at the launch site in North Korea's northeast.

In Australia, visiting South Korean President Lee Myung-bak said North Korea was ramping up its threats to achieve "a more positive position" at the negotiating table with President Barack Obama's administration over a nuclear disarmament-for-aid deal.

Relations between the two Koreas — which technically remain at war because their three-year conflict ended in 1953 with a truce, not a peace treaty — have sunk to their lowest level in years since Lee took office a year ago with a hard-line stance toward North Korea.

Incensed by Lee's tough policy, the North cut off reconciliation talks and in late January declared it would no longer honor a nonaggression pact and other peace agreements.

In Tokyo, U.S. envoy Stephen W. Bosworth and Japan's main envoy to the nuclear talks Akitaka Saiki, urged the North "not to take an action that would harm the region's peace and stability," Japan's Foreign Ministry said in a statement.

The two envoys said a launch — even of a satellite — would violate U.N. Security Council resolutions banning the North from engaging in ballistic activity, the ministry said. Japanese officials say Tokyo may seek additional sanctions against North Korea in case of a launch. Defense Minister Yasukazu Hamada indicated that it could use a missile shield to shoot one down.