LAS VEGAS — A gunman opened fire in the lobby of a federal building in downtown Las Vegas this morning, killing one court officer and wounding a second before he was shot to death.

The gunfire erupted moments after 8 a.m. and lasted for several minutes. Shots echoed around tall buildings in the area, more than a mile north of the Las Vegas Strip. An Associated Press reporter on the eighth floor of a high-rise building within sight of the building heard more than 20 shots during the sustained barrage of gunfire.

The U.S. Marshals Service said the victims included a deputy U.S. marshal and a court security officer. The 48-year-old deputy marshal was hospitalized, and the 65-year-old security officer died.

FBI Special Agent Joseph Dickey said the gunman died across the street shortly after the shootout. The man's identity and motive were not immediately known.

Authorities believe the shooter acted alone, Chief Deputy U.S. Marshal Roxanna Lea Irwin said.

The building was evacuated, police and news helicopters circled overhead, and Las Vegas police cordoned off the area for several blocks. A 16-story state and local courthouse two blocks away was locked down as a precaution.