A left-wing protester in the Gazi district of Istanbul throws a molotov cocktail toward a police vehicle during a demonstration against a state operation against Kurdish militants. (Yasin Akgul/AFP/Getty Images)

Turkish warplanes struck Kurdish militants in northern Iraq early Saturday, expanding and complicating the air war launched by Turkey against the Islamic State in Syria the day before.

The strikes targeted weapons-storage facilities and camps belonging to the outlawed Kurdistan Workers Party, or PKK, at its Mount Qandil headquarters in the remote mountains of Iraqi Kurdistan, according to a government statement.

There were also strikes for a second night in a row against the Islamic State in Syria, indicating that Turkey is now actively engaged in the war against the militants after months on the sidelines.

The strikes against Kurds in Iraq opened a second front for Turkey, effectively ending a two-year truce with the PKK that had been a signature achievement of then-Prime Minister Recep Tayyip Erdogan’s government.

The PKK issued a statement saying that the cease-fire, which had already been strained by a number of PKK attacks in Turkey, is now off. “This truce has no meaning anymore,” it said.

The Turkish government has repeatedly maintained that it regards the Islamic State and the PKK as equally culpable of terrorism. Now that Turkey is bombing both of them, authorities are braced for a potential wave of retaliatory attacks by either.

The targeting of Kurdish militants will also complicate the United States’ air war against the Islamic State, which has relied heavily on a PKK-allied group of Syrian Kurds to make advances in northern Syria.

The United States, like Turkey, has designated the PKK a terrorist organization, but unlike Turkey it does not apply the label to the PKK’s Syrian affiliate, the Democratic Union Party, or PYD, thereby making cooperation possible.

In a series of comments on Twitter, Senior State Department official Brett McGurk said that the Turkish strikes against the Kurds had no connection to the U.S. deal with Turkey under which American warplanes will be permitted to use Turkish bases to launch attacks against the Islamic State. He urged both parties to return to the peace process, but also acknowledged Turkey’s “right to self-defense.”

“We have strongly condemned the PKK’s terrorist attacks in Turkey and we fully respect our ally Turkey’s right to self-defense,” tweeted McGurk, who serves as the deputy special presidential envoy to the anti-Islamic State coalition.

“There is no connection between these airstrikes against PKK and recent understandings to intensify US-Turkey cooperation against ISIL,” he added, using an acronym for the Islamic State.

So keen was the Obama administration to secure Turkish cooperation against the Islamic States that it would be unlikely to object to Turkey also taking on Kurdish militants, said Soner Cagaptay of the Washington Institute for Near East Policy.

“Turkey just pulled the carpet from under the Kurds,” he said. “In the name of fighting terrorism . . . Turkey now has carte blanche to act against the PKK because it is also is acting against ISIS.”

The attacks stirred up tensions between Turkey and Kurdish groups across the complex spectrum of alliances and rivalries spanning the territories in Turkey, Iraq and Syria that Kurds claim as their homeland.

PYD leader Saleh Muslim said he did not expect the Turkish attacks on the PKK to affect directly the group’s operations in Syria or its collaboration with the United States. “There is no PKK in Rojava,” he said, using the name applied by Kurds to the territory they claim in northern Syria and rejecting an allegation frequently made by Turks and Syrian Arabs that the PKK is deeply engaged in the battles there.

He said the bombings in northern Iraq call into question Turkey’s embrace of the fight against the Islamic State and suggested that Turkey had agreed to participate in the U.S.-led war as an excuse to take on the Kurds. The agreement with the United States includes permission for U.S. warplanes to use Turkish territory to launch attacks against the Islamic State.

“I think it’s a kind of show to say, ‘I am against Daesh.’ I think they are not sincere,” Muslim said, using the Arabic acronym for the Islamic State.

“All the world knows the Kurds are fighting against Daesh. Even the PKK is fighting against Daesh in northern Iraq. So what they are doing is a kind of support to Daesh because they don’t want PKK to fight against Daesh in Iraq.”

Tensions also surfaced between the Turkish government and Massoud Barzani, the president of the Iraqi region of Kurdistan where the PKK bases were hit. Barzani is no ally of the PKK, but his government has tolerated for decades the presence of PKK camps in the inaccessible mountains in territories bordering Iraq, Iran and Turkey that are beyond the reach of authorities in any of those countries. Some PKK fighters have fought alongside U.S.-allied Kurdish forces in battles against the Islamic State in Iraq.

Turkish Prime Minister Ahmet Davutoglu told reporters in Ankara that Barzani “expressed his solidarity” with Turkey in an hour-long telephone conversation Saturday morning. A statement from Barzani’s office said however that the Kurdish leader had “expressed his displeasure” with the air raids.

The strikes came at the end of a week of violence in which the PKK in Turkey as well as the Islamic State had carried out attacks. The PKK has long accused Turkey of cooperating with Islamic State militants, and after a suicide bomber killed 30 people at a gathering of Kurds in the southern Turkish town of Suruc, the Kurdish group retaliated by shooting two Turkish policemen.

In anticipation of further domestic violence, Turkish police have detained nearly 600 suspected Islamic State, Kurdish and other leftist militants in nationwide raids over the past two weeks.

Turkey had regularly bombed PKK targets in northern Iraq throughout the latter years of the last decade with the approval of the United States, which controlled Iraqi airspace at the time. The last strikes were in 2011.

The Turkish government’s statement said Turkey had informed its NATO allies and the United Nations ahead of the strikes in Iraq.

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Today's coverage from Post correspondents around the world