An armed hijacker seized control of a Colombian jetliner Monday and diverted it to Panama after releasing 135 passengers and crew members, officials said.

Eduardo Guerrero, administrator of Omar Torrijos International Airport, said the man was carrying two hand grenades and at least one pistol and was holding the pilot, co-pilot and a flight engineer hostage.There were no passengers on board.

Speaking to reporters, Guerrero called the man "desquiciado" - Spanish for mentally unbalanced - and said a special negotiating team that talked with him on a ground-crew intercom could not learn his identity, nationality or what he wants.

The hijacker forced the airliner's crew to cut off communications with the airport control tower after the plane landed, Guerrero said. But he said a three-man negotiating team walked up to the plane and spoke through the intercom.

An hour after the plane landed, its engines were still running. Guerrero said he did not know why.

Guerrero said the negotiating team is made up of Panamanian Air Force Capt. Miguel von Siedlitz, chief of security at the airport; Luis Rossi, director of all Panamanian airports; and Maj. Fitz Gibson of the Panamanian Defense Forces.

He said a special Defense Force team was deployed around the plane. Soldiers could be seen in ditches about 80 yards from the jet.

The Avianca jet took off from the Colombian city of Medellin Monday morning on a flight to Bogota, about 200 miles to the southeast, and was hijacked, the security chief of Colombia's Civil Aeronautics Administration told the radio network Caracol.

Capt. Edgard Lozano told the radio in Bogota that the plane was forced back to Medellin, where 129 passengers and six flight attendants were freed.

The Boeing 727 then took off for Panama, where it landed at the international airport outside Panama City and taxied to a stop on the grass next to an isolated runway. Reporters and most officials were kept about 600 yards away.

Guerrero said it appeared the plane would be refueled.

In Medellin, several passengers spoke to radio Caracol. "Everything happened very fast, but there was no panic," said one passenger, Luis Fernando Piedrahita.

He said the hijacker was a young man. The hijacker carried a briefcase that he said contained hand grenades, Piedrahita said.

Another passenger, Javier Robledo, said he was sitting next to the hijacker.

The young man gave a note to a flight attendant, and she led him to cockpit, Robledo told Caracol.

"Both the hijacker and the flight attendant were very nervous," Robledo said. "Nothing happened, and 10 minutes after going back to the airport the pilot told everyone they should get off the plane."