Updated

North Korea warned that the massing of U.S forces in the region increases the danger of nuclear war as a U.S. aircraft carrier anchored off South Korea on Saturday.

South Korean President Roh Moo-hyun told his military to prepare for the possibility that North Korea might attempt minor provocations during U.S.-South Korean military exercises that will involve the USS Carl Vinson, South Korean news agency Yonhap said.

Roh's office could not immediately confirm the report Saturday evening.

North Korea's main state-run newspaper, Rodong Sinmun, said Saturday, "the U.S. can attack the DPRK any moment," using the acronym for North Korea's official name, Democratic People's Republic of Korea.

"The U.S. seeks to round off its preparations for a nuclear war against the DPRK at its final phase and mount a pre-emptive nuclear attack on it any time," it added.

Tensions have risen since October, when U.S. officials said North Korea admitted having a uranium program. Washington and its allies suspended fuel shipments; the North retaliated by expelling U.N. monitors, withdrawing from the Nuclear Nonproliferation Treaty and restarting a nuclear reactor that had been mothballed for years under U.N. seal.

Capt. Richard B. Wren said the U.S. warship was here "as a show of solidarity" with South Korea and to provide a "deterrence."

"Certainly our presence in the region is not in direct response on North Korea, but certainly our presence can also be an influence," he said.

Navy Capt. Donald P. Quinn, commander of Carrier Air Wing Nine, said "there are greater tensions, which means we have to be better at what we do."

The carrier has 70 aircraft, a fleet of supporting warships and more than 5,000 sailors and marines. It is in South Korea for the joint military exercises, named Foal Eagle, which began early this month. On Saturday, the carrier was moored just outside the breakwater of Pusan harbor on South Korea's southeast coast.

The forces were joined by six U.S. F-117 Nighthawk stealth fighters deployed to an air base in South Korea.

The Pentagon also recently sent a dozen B-52 bombers and a dozen B-1 bombers to the Pacific island of Guam as a precautionary move.

Pyongyang has objected to the war games, saying they are a rehearsal for invasion.

Some time in the next few days, the Carl Vinson plans to steam up the coast to support a landing exercise by U.S. and South Korean marines near the port of Pohang, where U.S. troops landed for the 1950-53 Korean War.

In recent weeks, North Korea has escalated tensions by test-firing two short-range missiles and intercepting a U.S. reconnaissance plane off the country's east coast.

Meanwhile, in Berkeley, Calif., North Korea's U.N. ambassador met with officials from South Korea, the United States, China, Japan and the European Union for talks aimed at allaying tensions on the Korean Peninsula. However, no one was appearing as an official representative of a country.

"We are having a very lively discussion," said Yoshinobu Yamamoto, a University of Tokyo professor and co-chair of the conference.

The Japanese government, meanwhile, has said it is considering strengthening its missile defenses amid reports that North Korea is preparing to test a medium-range missile capable of reaching Japan.

South Korea's military Saturday said it did not believe North Korea was preparing to test-fire its ballistic missiles.

The Tokyo announcement came a day after Japan's Defense Agency said it had deployed an Aegis-equipped destroyer -- which carries top-of-the-line surveillance systems and ship-to-air missiles -- in the waters between Japan and North Korea.

Japan's Kyodo news agency reported Friday that the government was considering sending two more Aegis-equipped destroyers to the waters in response to the possible threat.