ANKARA (Reuters) – Turkish warplanes hit Kurdish militant targets in northern Iraq on Wednesday and killed six militants, the military said, in a second day of cross-border raids.

A military statement said the air strikes targeted the Zap region, the Turkish name for a river which flows across the Turkish-Iraqi border and is known as Zab in Iraq.

The air strikes hit “two hiding places and one shelter, and killed six separatist terrorist organisation militants who were understood to be preparing an attack,” the statement said.

The raids were part of a widening campaign against the outlawed Kurdistan Workers Party (PKK) which has also hit other Kurdish fighters inside Iraq – apparently by accident.

On Tuesday, Turkish planes bombed Kurdish targets in Iraq’s Sinjar region and northeast Syria, killing about 70 militants inside the two neighbouring states, according to a Turkish military statement.

The United States expressed “deep concern” over those air strikes and said they were not authorized by the U.S.-led coalition fighting Islamic State.

Five members of the Iraqi Kurdish peshmerga forces, which are also deployed in Sinjar, were killed. Kurdish authorities who run their own autonomous region in north Iraq enjoy good relation with Turkey and, like Ankara, oppose the presence of a PKK affiliate in Sinjar.

Turkish President Tayyip Erdogan on Tuesday told Reuters that he would not allow Sinjar to become a PKK base, adding that Ankara informed its partners including the United States, Russia and Iraqi Kurdish authorities ahead of the operation.

On Wednesday, Turkish foreign ministry spokesman Huseyin Muftuoglu said the parties were informed through both military and diplomatic channels.

Turkey had passed on information to the United States and Russian military attaches in Ankara, Muftuoglu said, and Turkish army chief Hulusi Akar also held a telephone conversation with his U.S. and Russian counterparts.

The Combined Air Operations Center in Qatar, responsible for providing command and air control in regions including Iraq and Syria, was also informed in advance, Muftuoglu said.

Designated a terrorist group by Turkey, the United States and the European Union, the PKK has waged a three-decade insurgency against the Turkish state for Kurdish autonomy. More than 40,000 people have been killed in the conflict, most of them Kurds.

The army also reported on Wednesday cross-border mortar fire from two areas inside Syria — one believed to be under the control of Syrian government forces and the other by Kurdish YPG militants. It said there were no casualties, and it retaliated.

(Reporting by Ece Toksabay and Tuvan Gumrukcu in Ankara and Humeyra Pamuk in Istanbul; Editing by Dominic Evans and Angus MacSwan)