HANOI – North Korea said today it will counter U.S. and South Korean joint naval exercises with “nuclear deterrence” after the Obama administration said the government in Pyongyang shouldn’t take any provocative steps.

North Korea will “legitimately counter with their powerful nuclear deterrence the largest-ever nuclear war exercises to be staged by the U.S. and the South Korean puppet forces,” the National Defense Commission said, according to the Korean Central News Agency.

The maneuvers, which involve 20 vessels and 200 aircraft from the United States and South Korea, pose a threat to the country’s sovereignty and security, Ri Tong Il, an official with North Korea’s delegation to the Asean Security Forum, told reporters in Hanoi on Friday.

Ri’s comments came after North Korean Foreign Minister Pak Ui Chun sat in the same room with Secretary of State Hillary Clinton for a security meeting of Asia’s largest powers.

Clinton condemned North Korea for being “on a campaign of provocative, dangerous behavior,” urging Kim Jong Il’s regime to change.

Still, the “door remains open for North Korea,” Clinton later told reporters. “We are willing to meet with them, willing to negotiate, to move toward normal relations” if North Korea commits itself to giving up its nuclear weapons program.

The United States said this week it will intensify sanctions against North Korea and conduct military exercises with South Korea in waters surrounding the peninsula. The USS George Washington, a nuclear-powered aircraft carrier, and three destroyers called at South Korean ports this week in a show of force.

“North Korea may very well go ahead with missile launches or even a third nuclear test to show it won’t bend to U.S. pressure,” said Yang Moo Jin, a professor at the University of North Korean Studies in Seoul. “North Korea must have sensed that the U.S. and South Korea are after its regime’s collapse.”

Four officers of Japan’s Maritime Self-Defense Force will board a U.S. ship as observers for the joint military exercise, planned for Sunday through Wednesday in the sea between South Korea and Japan, said Yoshito Sengoku, chief cabinet secretary.

Ri said the George Washington’s presence threatened security on the peninsula, which has been divided for more than half a century. Pak maintained the need for a peace treaty to replace a cease-fire, signed in 1953, to guarantee the peninsula’s security, Ri said.

“It’s no longer the 19th century with gunboat diplomacy,” Ri said. “It is a new century and the Asian countries are in need of peace and development.”

An international panel concluded that the March 26 sinking of the Cheonan was caused by a torpedo fired from a North Korean mini-submarine. The United Nations Security Council condemned the attack, which killed 46 sailors, without naming a culprit.

The investigation’s results have been “fabricated,” Ri said, adding that North Korea wouldn’t apologize for the incident as demanded by South Korea.