The sixth announced nuclear weapons test of the year was detonated 1,000 feet beneath the surface of the Nevada desert Thursday, a Department of Energy spokesman said.

The test, code-named "Ledoux," had a yield of less than 20 kilotons and was buried beneath the surface of Yucca Flat, some 75 miles northwest of Las Vegas.Energy Department spokesman Chris West said no radiation was released as a result of the 11:02 a.m. test.

"This was, from all indications a successful test," West said.

He said the weapon was a relatively small one and no earth motion was felt by residents in Las Vegas.

At this time last year, the Energy Department had conducted eight announced tests at the Nevada Test Site.

This was the 500th test announced by the United States since the signing of the Limited Test Ban Treaty in 1963. The treaty prohibits above-ground testing.