An explosion at Istanbul’s Sabiha Gokcen airport wounded two cleaning staff on a plane, but the cause of the blast was not clear, Pegasus airline said on Wednesday.

Pegasus said the blast occurred at 2:05 am (7.05 p.m. Et Tuesday) when no passengers were in the area and that operations were continuing normally.

Police armed with rifles and protective vests imposed tight security at entrances to the airport after the blast, searching vehicles in the area while a police helicopter circled overhead, state-run Anadolu Agency said.

It said one of the cleaners was seriously hurt, suffering a wound to the head, while one was wounded in the hand, and they were both being treated in hospital.

The Sabiha Gokcen airport operator said in a brief statement there was no problem with plane takeoffs and landings at the airport, adding that investigations into the cause of the blast were continuing. Reuters