A Kurdish militant group has claimed responsibility for an attack at Istanbul's second airport that killed a cleaner, and threatened more assaults.

In a statement posted on its website Saturday, the Kurdistan Freedom Falcons — an offshoot of the Kurdistan Workers' Party, or PKK — said it attacked Sabiha Gokcen Airport with mortar guns.

It said the Dec. 23 attack was in retaliation for the government's stepped-up military operations against the PKK.

Turkish authorities have not disclosed the cause of the pre-dawn explosion at the airport, which also injured another cleaner and damaged three planes, saying it is still under investigation.

Turkish security forces last week launched a large-scale operation to rout militants linked to the PKK in mostly Kurdish districts. More than 180 rebels were killed.