(AP) LAS VEGAS, Colo. Investigators believed ammonia was what sickened 11 people who were on board a plane from Denver to Las Vegas over the weekend.

One-hundred-43 passengers and the crew on Ted Flight 1491 were quarantined for several hours late Saturday night at McCarran International Airport in Las Vegas. Hazardous materials experts were checking the aircraft.

A portion of the airport was also closed.

Elaine Sanchez, a spokeswoman for McCarran International Airport, said that four of the victims were flight attendants.

A passenger on the flight, Don Yarbrough, said that investigators believe the victims reacted to a cleaning fluid containing ammonia.

(CBS4) DENVER A United Airlines flight from Denver was held in Las Vegas Saturday night after at least three flight attendants and a passenger reported feeling sick.

United spokeswoman Robin Urbanski said that when Flight 1491 landed in Las Vegas as scheduled, the crew reported that three flight attendants and the passenger felt weak and nauseated.

Urbanski said authorities in Las Vegas took over the aircraft and released it back to the airline around 10:30 p.m. There were 143 passengers and crew on board. There are no details of the quarantine or what made people feel sick.

Airport authorities told CBS4 a total of 11 people got sick during the flight.

Two searches of the plane turned up nothing. United has parked the plane while it conducts its investigation.