U.S. & World

SEOUL, South Korea (CBS) ― North Korea vowed Thursday to enlarge its atomic arsenal and warned of a "fire shower of nuclear retaliation" in the event of a U.S. attack, as the regime marked the 1950 outbreak of the Korean War.

The anniversary came as the U.S. Navy trailed a North Korean ship suspected of carrying weapons in violation of a U.N. resolution punishing Pyongyang's May 25 nuclear test, and as anticipation mounted that the North might test-fire short- or mid-range missiles in the coming days.

"North Korea is upping the ante with each nuclear and missile test, and appears to be rejecting efforts to return to the Six-Party talks," said CBS News foreign affairs analyst Pamela Falk at the United Nations.

"Recognizing the gravity of the crisis, President Obama on Wednesday issued a continuation of the National Emergency with regard to North Korea," Falk added.

President Obama extended U.S. economic sanctions against North Korea for another year Wednesday, saying the North's possession of "weapons-usable fissile material" and its proliferation risk "continue to pose an unusual and extraordinary threat" to the United States, according to the White House Web site.

State-run newspapers in Pyongyang ran lengthy editorials accusing the U.S. of invading the country in 1950 and of looking for an opportunity to attack again. The editorials said that justified North Korea's development of atomic bombs to defend itself.

The North "will never give up its nuclear deterrent ... and will further strengthen it" as long as Washington remains hostile, Pyongyang's main Rodong Sinmun newspaper said.

In a separate commentary, the Rodong blasted a recent U.S. pledge to defend South Korea with its nuclear weapons, saying that amounted to "asking for the calamitous situation of having a fire shower of nuclear retaliation all over South Korea."

The Minju Joson, another state-run newspaper, said the U.S. should withdraw its troops from South Korea and drop its "hostile" policy toward the North, saying those were "key to resolving the Korean peninsula issue."

Historical evidence shows it was North Korea that started the Korean War by invading the South, but Pyongyang claims the U.S. was to blame. The totalitarian government apparently hopes to infuse North Koreans with fear of a fresh American attack to better control the hunger-stricken population.

The U.S. fought alongside the South, leading U.N. forces, during the war. The conflict ended in 1953 with a truce, not a peace treaty, leaving the peninsula divided and in a state of war. The U.S. has 28,500 troops in South Korea to protect against hostilities.

The North accused Washington Wednesday of seeking to "provoke a second Korean War" as the regime prepared to hold maritime military exercises off its eastern coast.

The U.S. has repeatedly said it has no intention of attacking the North.

The new U.N. resolution seeks to clamp down on North Korea's trading of banned arms and weapons-related material by requiring U.N. member states to request inspections of ships carrying suspected cargo.

North Korea has said it would consider interception of its ships a declaration of war.

The U.S. has been seeking to get key nations to enforce the sanctions aggressively. Secretary of State Hillary Rodham Clinton called the foreign ministers of Russia and China on Wednesday to discuss efforts to enforce the U.N. punishments, State Department spokesman Ian Kelly said.

On Tuesday, Obama called Australian Prime Minister Kevin Rudd and discussed how to ensure the U.N. sanctions are fully implemented, the White House said in a statement Wednesday.

The Kang Nam is the first North Korean ship to be tracked under the resolution. It left the North Korean port of Nampo a week ago and is believed bound for Myanmar, South Korean and U.S. officials said.

Myanmar state television on Wednesday evening said another North Korean vessel was expected to pick up a load of rice and that the government had no information about the Kang Nam.

A senior U.S. defense official said Wednesday that the ship had already cleared the Taiwan Strait.

He said he didn't know how much range the Kang Nam has - whether or when it may need to stop at a port to refuel - but that the ship has in the past stopped in Hong Kong.

Another U.S. defense official said he tended to doubt reports that the Kang Nam was carrying nuclear-related equipment, saying the information officials had received seemed to indicate the cargo was conventional munitions.

The U.S. officials spoke on condition of anonymity because they were discussing intelligence.

The U.S. and its allies have not decided whether to contact and request an inspection of the ship, Pentagon press secretary Geoff Morrell said Wednesday. He said he did not believe a decision would come soon.

Reports about possible missile launches from the North highlighted the tension on the Korean peninsula.

The North has designated a no-sail zone off its east coast from June 25 to July 10 for military drills.

A senior South Korean government official said the ban is believed connected to North Korean plans to fire short- or mid-range missiles. He spoke on condition of anonymity, citing department policy.

South Korea's Yonhap news agency reported that the North may fire a Scud missile with a range of up to 310 miles or a short-range ground-to-ship missile with a range of 100 miles during the no-sail period.

U.S. defense and counterproliferation officials in Washington said they also expected the North to launch short- to medium-range missiles. The officials spoke on condition of anonymity to discuss sensitive intelligence.

North Korea had warned previously it would fire a long-range missile as a response to U.N. Security Council condemnation of an April rocket launch seen as a cover for its ballistic missile technology.

(© 2009 CBS Broadcasting Inc. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)