PHOENIX — Three environmental groups filed a lawsuit Monday against U.S. Interior Secretary Dirk Kempthorne for authorizing uranium exploration on 1 million acres of public land near the Grand Canyon.

The Center for Biological Diversity, the Grand Canyon Trust and the Western Mining Action Project filed the suit in U.S. District Court. Also named as defendants are the Department of Interior and U.S. Bureau of Land Management.

Department of Interior spokesman Chris Paolino said it's department policy to not comment on pending litigation.

The environmental groups say Kempthorne defied a House committee resolution protecting 1 million acres near the Grand Canyon from new uranium mining by continuing to authorize uranium exploration.

The House Natural Resources Committee in June passed a measure 20-2 after Republicans walked out of the hearing in protest. The measure required Kempthorne to stop issuing new mining claims, but an Interior official argued in a letter sent to the committee chairman that the resolution couldn't stand because the committee lacked a quorum.

The Interior Department letter from congressional and legislative affairs Director Matt Eames said the committee needed 25 members present to act on the measure and fell three votes shy.

As a result, he wrote, "we do not believe that the resolution constitutes a notification of the committee, as required under the statute."

Since the resolution passed, four new mining claims were filed and four notices for uranium exploration were accepted along the Arizona strip, the part of the state north of the Colorado River, said Scott Florence, director of the Bureau of Land Management's Arizona strip district.

He said most, if not all, of the claims and notices were on the land specified in the resolution.