Japan will file a "fierce" protest and seek an immediate U.N. Security Council meeting if North Korea test-fires a long-range missile, Tokyo's foreign minister said Sunday, amid increasing reports that a launch may be imminent.

Meanwhile, North Korea said Sunday it is seeking to increase its military deterrent to cope with U.S. moves in a restatement of its typical anti-Washington propaganda.

There was no mention of a missile in the report from North Korea's official media on a national meeting marking the anniversary of North Korean leader Kim Jong Il starting work in the country's communist party.

North Korea hasn't fired a long-range missile since August 1998, when it sent a rocket flying over parts of Japanese territory in a launch that shocked the region. Since 1999, Pyongyang has abided by a self-imposed moratorium on long-range tests.

But signs of a launch have grown in recent days, with reports saying a missile has been assembled at a launch pad on the North's eastern coast and that it may have been fueled for launch.

"There are signs" of a missile launch, Jung Tae-ho, a spokesman at the South Korean president's office, told The Associated Press, without elaborating. He said security officials were "closely watching the situation."

South Korea's Yonhap news agency, citing a South Korean government official, reported that weather conditions in the region of the North Korean launch site weren't good, indicating the North may not fire its missile Sunday.

Satellite weather images posted on the Web site of the South's Korea Meteorological Administration showed clouds around the launch site in northeastern North Korea as of about 6 p.m.

A missile launch "depends a lot on weather conditions," a South Korean intelligence official told The Associated Press, but he didn't comment on weather conditions in the area.

With such weather, if there was no particular movement by 8 p.m. "we can say a missile won't be launched today," Yonhap quoted an unidentified Foreign Ministry official as saying.

A nighttime launch is considered unlikely.

Japanese Foreign Minister Taro Aso said his country would not immediately resort to arms if North Korea fires a missile, but would take the issue to the United Nations.

"We will naturally file a stern protest and it will be fierce," Aso said on a news program on TV Asahi, adding that the North would gain nothing from the test.

Aso also reportedly said that it would be "inevitable" that the Security Council would consider imposing sanctions on Pyongyang if it goes ahead with the missile launch.

Speaking on another news program on Fuji TV, Aso said Tokyo could impose sanctions on the North in the event a missile was fired because it would violate Pyongyang's commitment to impose a moratorium on such tests.

At the North Korean national meeting Sunday, officials talked about increasing the North's "military deterrent" -- commonly used by the country to refer to its nuclear program, which Pyongyang contends it needs for a defense to a possible U.S. attack. Washington denies any intention to invade.

"The [North] Korean army and people will do their best to increase the military deterrent with sharp vigilance to cope with the moves of the U.S., which is hell-bent on provocations for war of aggression on the DPRK, resorting to its anti-DPRK policy, and its followers Japan and other bellicose forces," said the report from the Korean Central News Agency, quoting Choe Thae Bok, secretary of the Central Committee of the Workers' Party of Korea.

DPRK refers to the Democratic People's Republic of Korea, the North's official name.

"If the enemies ignite a war eventually, the Korean army and people will mercilessly wipe out the aggressors and give vent to the deep-rooted grudge of the nation," Choe said.

The U.S. and Japan have confirmed that assembly of what is believed to be a Taepodong-2 missile has been completed with two stages at the launch site, based on photos from satellites, Japan's largest daily, the Yomiuri newspaper, reported Sunday.

The Taepodong-2 missile is believed to be the North's most advanced model with the capability to reach the United States with a light payload.

The paper also said it appeared North Korea has begun filling the missile with fuel, citing unnamed U.S. government officials who conveyed information Saturday to the Japanese government through unofficial channels.

Yonhap, citing diplomatic sources in Washington, also reported there was a possibility the missile may have already been fueled, with satellite photos showing tens of fuel tanks at the launch site.

The missile concerns come amid an extended impasse at international talks on the North's nuclear weapons program, which haven't met since November. The North has claimed it has a nuclear weapon, but it isn't believed to have a design that would be small and light enough to place on top of a missile.