BERLIN (AP) — Lufthansa says six airport workers have suffered minor injuries from smoke inhalation when a vehicle pulling a jet to a gate caught on fire.

Lufthansa told the dpa news agency that it was still not clear how the fire broke out Monday morning at Frankfurt Airport, but that the cockpit of the empty passenger aircraft was seriously damaged by the heavy smoke.

The fire sent black smoke billowing in the air but airport traffic was not affected by the incident.