A day after announcing it will reactivate frozen nuclear facilities, North Korea accused the United States on Friday of piracy in the seizure of a ship carrying missile shipments to Yemen.

On Thursday, North Korea said it would immediately revive a Soviet-designed nuclear power plant the United States and its allies suspect was being used to develop nuclear weapons before it was frozen in 1994.

This week, Spanish warships seized a North Korean ship carrying at least 15 short- and medium-range Scud missiles in the Arabian Sea. The U.S. military took charge of the ship, but then allowed it to sail on after high-level diplomacy between the United States and Yemen.

"This is an unpardonable piracy that wantonly encroached upon the sovereignty of the DPRK," an unidentified spokesman for the North Korean Foreign Ministry said in comments reported by the North's Korean Central News Agency. DPRK stands for the Democratic People's Republic of Korea.

"The U.S. captured the DPRK trading cargo ship Sosan in broad daylight when the ship was sailing in the open seas off Yemen on Dec. 10. The U.S. even mobilized warships and warplanes of Spain for the capture," the spokesman said.

"Soon after it was brought to light that its capture had no legal ground but wantonly violated the routine trade between countries, the U.S. was compelled to send the ship back," he said. Missile exports are a major source of foreign currency for the impoverished communist country.

There was no immediate reaction from the White House to North Korea's latest statements.

The United States let the intercepted shipment proceed to Yemen after receiving assurances the Scuds would not be transferred elsewhere in the tense Persian Gulf region.

Bush administration officials acknowledged that boarding the ship and taking charge of its cargo probably violated international law. But administration decision-makers were guided by concern about an influx of weapons into the Persian Gulf region just as the United States is considering force to disarm Iraq.

However, North Korea's declaration that it will restart a frozen plutonium-based nuclear reactor and resume construction on other nuclear facilities posed a new quandary for the United States and its allies.

With a bitter winter ahead, North Korea said it had no choice but to reactivate the reactor and resume construction of other nuclear facilities to supply desperately needed power after a U.S.-led decision last month to suspend annual oil shipments of 500,000 tons.

The suspension was designed to pressure North Korea to give up a more recent nuclear program based on uranium enrichment. The oil was a provision of a 1994 U.S.-North Korean deal that froze the earlier nuclear program, which was at the center of a crisis that nearly led to war on the Korean Peninsula.

In response to North Korea's decision to lift the freeze on the earlier program, a spokesman for President Bush called the situation "regrettable" but said the United States had no plans for military action. U.S. officials say they want to use diplomatic means to pressure North Korea to abandon its nuclear ambitions.