FRANKFURT, June 11 (Xinhua) -- A tow truck caught fire at Frankfurt airport Monday morning, while pulling an empty Airbus A340-300 aircraft to a boarding gate, slightly injuring six people, German media Spiegel reported, citing a Lufthansa spokesperson.

Smoke was widely visible around 8 a.m. local time (0600 GMT), badly burning the truck.

Lufthansa's wide-body aircraft painted with Star Alliance pattern, which should have operated as flight LH426 from Frankfurt to Philadelphia as planned, was also damaged.

As result, the flight was delayed by around 90 minutes and took off on different aircraft while the first was being inspected.

The cause of the fire remains unclear, while the extent of damage has yet to be determined, according to Lufthansa.