Two U.S. Air Force C-141 cargo planes collided in midair late Monday over Montana, apparently killing all 13 people aboard, while in a separate accident an Air Force B1-B bomber crashed in Texas.

      Four crew members from the bomber, which crashed in a remote West Texas mountain range while on a training mission, are still missing, Air Force officials said early Tuesday.The two Air Force C-141 cargo planes that collided at about 9:20 p.m. MST near Chinook, Mont., about 35 miles south of the Canadian border, were also on a training mission.

      "At the moment, our preliminary indication is that there are no survivors" in the cargo plane crash, Capt. Ray Martell, a spokesman at McChord Air Force Base in Washington where the planes were based, told Reuters early Tuesday.

      He said names of those aboard the cargo aircraft were being withheld pending notification of next of kin.

      Officials at McChord said the planes had been on a training exercise involving two other C-141s from McChord and a KC-135 tanker operated by the Washington Air National Guard out of Fairchild Air Force Base in Spokane.

      "The two other air crews reported seeing two separate fireballs (after impact)," said Air Force spokeswoman Capt. Anna Pilutti. She said a total of 13 crew members were on board the two planes at the time of collision and all were on active duty.

      Search and rescue teams were dispatched to the site of the accident, the Air Force said.

      Rescue workers in Texas continued their search Tuesday for four crew members who were on board the B1-B Bomber that crashed about 11 p.m. MST near Van Horn, Texas, about 120 miles southeast of El Paso, officials said.

      The bomber was based at Dyess Air Force Base in Abilene, Texas, and was on a training mission carrying no munitions at the time of the crash, Air Force Sgt. Beverly Jackson said.