The Soviet Union set off an underground nuclear blast at its Novaya Zemlya test site near the Arctic Circle Wednesday, ending its unilateral moratorium on nuclear testing.

The explosion at the island test site in the Bering Sea was the Soviet Union's first test in about a year. The device tested had a yield of between 20 and 150 kilotons in compliance with a testing threshold treaty, the official Tass news agency said.The Novaya Zemlya archipelago is the Soviet Union's second nuclear testing site. A ship from the environmental movement Greenpeace was boarded, detained and expelled from Soviet waters earlier this month for landing people on one of the islands to protest nuclear tests there.

Protests by local residents have shut down the Soviet Union's main site near Semipalatinsk in central Asia.

Wednesday's nuclear test came as Viktor Mikhailov, deputy minister of atomic energy, said the Soviet Union had been jeopardizing its security by observing a yearlong unilateral moratorium on testing while the United States continued such tests.

"Is this political risk justified in our time?" Mikhailov told the Communist Party newspaper Pravda. "The Soviet Union's unilateral nuclear disarmament can only lead to a U.S. monopoly."

Mikhailov's equation of a test ban with "nuclear disarmament" appeared to support U.S. claims that such explosions are necessary to ensure the reliability of atomic weapons, an assertion long refuted by Moscow.

Mikhailov accused the United States and its NATO allies of continuing to modernize their nuclear weapons, citing efforts to make their multiple-warhead rockets more precise and create weapons less vulnerable to anti-missile defenses.

The Western military alliance has also refused to follow the Soviet Union's pledge not to be the first to use nuclear arms in any confrontation, Mikhailov said.