California regulators on Monday suspended the charter certificate of the company that owned the tour bus that crashed in Arizona last week, killing seven Chinese tourists.

The California Public Utilities Commission did not elaborate on the suspension on its Web site. Requests seeking comment from the commission and the suspended company, D.W. Tour & Charter of San Gabriel, Calif., were not immediately returned.

The lead federal investigator for the crash said Monday that the company, which owns two buses and employs four drivers, passed its most recent federal review in August 2007. Six months earlier, a review showed the company had insufficient drug and alcohol testing and policies for drivers.

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Pete Kotowski, lead investigator for the National Transportation Safety Board, said D.W. Tour & Charter was considered a "satisfactory" carrier by federal standards at the time of the accident.

The 30-seat bus involved in the crash was smaller than a typical tour bus — similar in size to an airport car-rental shuttle — and did not have seat belts, he said. It was federally certified for travel on all U.S. highways, he said.

Investigators have been unable to speak to the 48-year-old hospitalized driver of the bus because of his injuries, Kotowski said.

In addition to the seven fatalities, the crash injured 10 passengers, authorities said. The accident occurred Friday near the Hoover Dam as the bus was returning to Las Vegas after a trip to the Grand Canyon.

The bus drifted onto the highway's shoulder and the driver overcorrected, sending it across two traffic lanes and into a gravel median, Kotowski said. It rolled over at least once before resting on its side. Most passengers were thrown out of the vehicle's windows.

Kotowski did not say how fast the bus was traveling. The speed limit on the straight stretch of road is 65 mph.

Tourists on the bus were Chinese nationals who had flown from Shanghai to San Francisco and had most recently been in Las Vegas, the Arizona Department of Public Safety has said.