ANKARA, Turkey (AP) — Turkey’s air force attacked 28 suspected Kurdish rebel targets in northern Iraq, the military said Friday, in a second day of cross-border strikes in retaliation for stepped up attacks by the guerrillas.

Nearly 100 rounds of artillery also were fired as the warplanes bombed sites on Thursday in the largely mountainous areas just across the border with Iraq as well as on Mount Qandil on the Iraqi-Iranian border, the military said.

In Wednesday’s attacks, the air force targeted 60 sites in northern Iraq, which rebels of the Kurdistan Workers’ Party, or PKK, use as a springboard for hit-and-run attacks in Turkey.

No casualties were immediately reported, but the military released aerial images of the sites it targeted, purporting to show PKK shelters, road blocks, anti-aircraft gun sites and ammunition depots.

In Iraq, PKK spokesman Ahmed Danis said nine Turkish warplanes bombed areas around the Iraqi provinces of Sulaimaniyah, Irbil and Dahuk near Turkey’s border, and that the targets were "former rebel bases." He said, "Our fighters left these bases a while ago and now they are in constant mobility. Therefore there were no casualties."

Turkey has vowed to toughen its fight against the group following a spate of attacks since July that have killed nearly 40 soldiers. A statement released after a meeting of the country’s Security Council late Thursday said Turkey would lead "a more effective, determined and result-oriented" drive against the rebels.

But that didn’t stop PKK. It attacked police and military stations in simultaneous overnight rocket strikes in Siirt province in southern Turkey, killing two soldiers and wounding three civilians, including a 15-year old, NTV news channel reported.

PKK is considered a terrorist organization by the United States and the European Union, and that was clear at the U.S. State Department, where spokeswoman Victoria Nuland confirmed Turkey’s latest attacks against "PKK terrorists" in northern Iraq.

"The United States recognizes the right of Turkey to defend itself against terrorist attacks," she told a news conference Thursday. She declined to comment on whether the U.S. would support any ground operation by Turkish forces.

Iraq’s government objected to Thursday’s airstrikes but also criticized the rebels for launching attacks aimed at Turkey from Iraqi territory.

The PKK is fighting for autonomy in the largely Kurdish areas of southeast Turkey. Tens of thousands of people have died in the conflict since 1984.

Turkey has carried out several cross-border airstrikes and ground incursions to fight the PKK in Iraq over the years, including aerial raids against suspected PKK hideouts last summer.