Updated

North Korea expressed rare gratitude Thursday for U.S. help in ending a high-seas standoff with Somali pirates, a sign of warming ties between the longtime foes fostered by progress on Pyongyang's nuclear disarmament.

The U.S. Navy's aid to North Korean sailors last week was unprecedented in the half century of hostility between the Cold War enemies, according to the Naval Historical Center in Washington.

The North's Korean Central News Agency hailed the maritime collaboration as a "symbol of cooperation" between the two countries "in the struggle against terrorism."

"The pirates' recent armed attack on our trading ship was a grave terrorist act perpetrated against a peaceful ship," KCNA said. "We feel grateful to the United States for its assistance given to our crewmen."

The last notable maritime encounter between the two countries was in 1968, when the North seized the USS Pueblo while it was on an intelligence-gathering mission off the North Korean coast and held 82 Americans as prisoners of war for 11 months.

The USS Pueblo is the only active-duty U.S. warship in the hands of a foreign power and remains on display as a tourist attraction in Pyongyang. Navy records show the ship was in international waters when it was captured, but North Korea insists it was inside the Korean coastal zone.

In a dramatic turnabout nearly four decades later, the U.S. Navy came to the aid of the North Korean cargo ship Dai Hong Dan, whose crew overpowered Somali pirates in a bloody battle.

After the crew regained control of the ship, Navy personnel boarded it at the North Koreans' invitation to treat wounded sailors and hijackers.

"This is a very interesting new direction between U.S. and North Korea," said Maochun Yu, a professor of history at the U.S. Naval academy. "It adds a little bit of complexity between the U.S. and North Korea. This one adds a human face, shows humanitarian aid is part of the U.S. mission."

In an unusually detailed report, the KCNA news agency said the USS James E. Williams and a helicopter rushed to the scene and "helped the (North Korean) sailors in fighting, threatening the pirates" via radio.

Seven pirates disguised as guards boarded the vessel on Oct. 29 while it was in port in Mogadishu, Somalia, KCNA reported. It said they demanded $15,000 and to be taken wherever they wanted.

The North Koreans fought back after seizing weapons from two pirates guarding the ship's engine room and regained control 20 hours after being taken captive, KCNA said. One pirate was killed.

"As shown by our crewmen through their actions, it is the disposition of the Korean people to fight out any terrorist act on the spot though they are empty-handed," the report said in the first public mention by the North of the episode.

Washington has downplayed the significance of its assistance to the North — even though the two countries remain technically at war since the Korean War ended in a 1953 cease-fire. The U.S. led a U.N.-authorized coalition in the three-year conflict, and 28,000 American troops remain deployed in South Korea.

"We fulfilled our responsibilities as a responsible member of international maritime organizations and treaties and responded to a distress signal on the high seas," State Department spokesman Sean McCormack said in response to the North's expression of gratitude.

It was the second time in two months that Pyongyang has thanked Washington, reflecting the friendly mood between the two countries spawned by progress in their prolonged standoff over the North's nuclear weapons programs.

In September, the North's Foreign Ministry issued a statement thanking the U.S. for providing emergency relief supplies after the worst floods in decades devastated the impoverished nation.

Pyongyang shut down its sole functioning nuclear reactor in July under a February deal with the United States, China, Japan, South Korea and Russia in exchange for political and economic concessions. It is now moving to disable is atomic facilities by year-end under watch of U.S. experts, meaning they will not be able to be quickly restarted.

One of the North's key demands in exchange for cooperating on disarmament has been to be removed from a U.S. blacklist of states that sponsor terrorism.

In Thursday's report on the ship hijacking, North Korea sought to advance such hopes.

"It is the consistent principled stand of the government to oppose all sorts of terrorism," KCNA said. "We will continue to render international cooperation in the fight against terrorism."

North Korea was put on the terror list for involvement in the 1987 bombing of a South Korean civilian jet that killed all 115 people aboard.