Peruvian officials said a fire truck that collided with a LATAM Airlines plane on a runway at Lima’s international airport was taking part in a nearby fire drill and entered the runway without authorization.

Flight LA2213, operated with an Airbus 320neo, was taking off from Lima’s airport for the city of Juliaca in southern Peru on Friday when the truck entered the runway and was hit by a wing of the plane. Part of the plane caught fire, but none of the crew or passengers were injured.

However, two airport firefighters in the truck were killed and a third was injured.

The firefighters were participating in a disaster response exercise, officials said in a news conference Saturday. They said the drill was part of the preparations for a new runway, scheduled to be ready next January.

“In the audios that we have, there was clearly no authorization for any vehicle to enter the runway,” said Jorge Salinas, president of the country’s aeronautical agency, Corpac. “This case was a runway incursion. We do not know why it happened, if the cause was human, mechanical or of nature? That is being investigated. Let’s not speculate.”

Lima’s Jorge Chavez International Airport had been scheduled to resume operations at 1 p.m. Saturday but extended the suspension of operations until midnight Sunday.

The Prosecutor’s Office is also investigating the accident.

There were 102 passengers and six crew members aboard the Airbus A320neo.

LATAM Airlines has said it lamented the death of the firefighters and would provide flexibility to reprogram flights to affected passengers at no extra cost. But it said it did not know why the firetruck was on the runway.

“No emergency was reported on the flight,” said LATAM Airlines Peru GM Manuel van Oordt. “It was a flight that was in optimal conditions to take off, it had authorization to take off and it encountered a truck on the runway, and we don’t know what the truck was doing there.”