MOSCOW — The Soviet Union carried out an underground nuclear blast in Soviet Kazakhstan on Saturday "in the interests of the national economy," the official Tass news agency said.
Tass gave no other details of its purpose. It said the blast had a yield of up to 20 kilotons, within the limits of the 1974 U.S.-Soviet Threshold Test Ban Treaty, and occurred in the Aktyubinsk region of northwestern Kazakhstan, a large Central Asian republic.
One kiloton is equal to the explosion of 1,000 tons of TNT.
Saturday's blast was the 17th since the Soviet Union ended a unilateral moratorium on nuclear explosions Feb. 28.
Soviet leader Mikhail S. Gorbachev had begun the moratorium in August, 1985.
Most of the explosions since Feb. 28 have been military tests, but the Soviets have said several were intended to help the economy.
U.S. and Soviet officials said Sept. 18, when they announced agreement in principle to eliminate their medium- and shorter-range nuclear missiles, that they would begin negotiations by Dec. 1 to ban all nuclear weapons tests.