ANKARA, Turkey — 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 predawn 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.

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