South Korea (search) urged the United States and its allies to be calm following North Korea's sudden declaration it is a nuclear power, reminding them that blustering and brinksmanship are nothing new in Pyongyang's toolbox of diplomatic tactics.

But South Korean officials also cautioned that North Korea could take further steps to raise tensions — such as shipping weapons materials to other countries with nuclear ambitions or even testing a bomb.

The North's announcement and its decision to pull out of six-nation disarmament talks was "a matter of grave concern," South Korean Foreign Minister Ban Ki-moon (search) told reporters in Washington, where he arrived on a previously scheduled trip to meet Secretary of State Condoleezza Rice.

But it is important to remember that "North Korea has shown similar attitudes in times of crucial negotiations" in the past, South Korea's Yonhap news agency quoted him as saying.

"We need to calmly analyze the situation," Ban said, noting the North's commitment to "solve the issue through dialogue and negotiations."

North Korea shocked the world by announcing Thursday that it has nuclear weapons and will stay away from U.S.-led six-nation nuclear disarmament talks.

In Seoul, Vice Foreign Minister Lee Tae-shik told members of the ruling Uri party that "the North's move appears to be aimed at improving its negotiating power."

But he warned "the problem could get very serious if North Korea takes additional actions," according to Uri Party spokesman Lim Jong-suk.

Since the nuclear crisis erupted in late 2002, North Korea has steadily increased stakes in the standoff. It first removed U.N. seals on its mothballed nuclear facilities, expelled the last U.N. nuclear monitors, then quit the Nuclear Nonproliferation Treaty, and later said it had completed reprocessing 8,000 spent fuel rods to extract weapons-grade plutonium.

South Korea's take on North Korea's announcement reflects its decades-long experience in dealing with North Korean officials, who pepper their negotiating rhetoric with shouts, threats and dire warnings of imminent clashes.

Around the region, governments voiced concern over the North's latest hardline maneuver and urged a resumption of six-nation talks aimed at persuading North Korea to abandon its nuclear weapons program in return for diplomatic and economic benefits.

In Australia, Prime Minister John Howard called North Korea's nuclear problem "one that has to be handled with a great deal of skill and balance."

"It's a quite dangerous situation," Howard told Nine Network television. "Now there's an element of bluff; I'm sure there's an element of exaggeration even if she does have some nuclear capacity."

Since 2003, the United States, the two Koreas, China, Japan and Russia have held three rounds of talks in Beijing, but no significant progress has been made.

Hopes for the resumption of talks rose in recent weeks after President Bush began his second term without using harsh words against the Stalinist regime. But to Pyongyang, Rice's labeling last month of it as one of the "outposts of tyranny" was insult enough to scuttle the diplomatic process.