WASHINGTON -- The Western Shoshone tribe and a group of Utah downwinders on Thursday filed a lawsuit in federal court in Las Vegas to prevent a 700-ton explosion scheduled June 2 at the Nevada Test Site.

Robert Hager, a Reno attorney who is representing the tribe and Utahns, said he is confident the court will issue a restraining order to block the explosion.

"I believe, based on the violations of the National Environmental Policy Act alone, the court will be required to enjoin the Defense Department from following through with this scheduled blast," Hager said in a phone interview.

The Nevada Division of Environmental Protection last week halted the test until the federal Defense Threat Reduction Agency showed the blast would comply with air quality standards and that hazardous particles would be tracked.

Hager said he understood the Nevada agency has withdrawn its objection to the test. Calls to the agency on Thursday were not returned.

"We continue to provide (the Nevada Division of Environmental Protection) the information requested so we can move forward (with the test)," Darwin Morgan, a test site spokesman, said Thursday.

The experiment will include the detonation of 700 tons of ammonium nitrate fuel oil solution in a 30-foot pit dug above one of the test site's tunnels about 100 miles northwest of Las Vegas.

Hager said the United Nations ruled in March that the Western Shoshones are the rightful owners of 60 million acres that include the test site. The downwinders are residents of Utah who might be affected by contaminated particles that might drift away from the test site after the blast.

"This blast would be the worst nightmare come true for downwinders because the most deadly substance known to man would be released into the atmosphere from the test site," Hager said.

Morgan disagreed.

"As stated in the environmental assessment, there are no contaminant soils in the area of the experiment," he said. "The explosion would simply bring into the atmosphere dust."

Hager said the tribe and downwinders are seeking unspecified damages.