The Kurdistan Workers Party, also known as the PKK, is a “terror group, plain and simple,” U.S. Vice President Joe Biden declared Saturday. Speaking after a roundtable meeting with various Turkish leaders in Istanbul, Biden appeared to dispel rumors the White House has been secretly working with PKK-linked fighters as a way to take on the Islamic State group, aka ISIS, Agence France-Presse reported.

“We want to make sure, because it’s such an important relationship — Turkey and the United States — that there’s no misunderstanding,” Biden said. He added ISIS, the PKK and the al Qaeda-linked al-Nusra Front were “simply terrorist groups and here in Turkey, they threaten and do harm and are of severe consequence to the interest of the people of Turkey.”

The PKK has waged a 30-year war against the Turkish government in a bid for more autonomy. About 40,000 people, most of them Kurds, have died in the conflict, BBC News reported. Peace talks between the PKK and Turkish officials broke down last year.

The U.S. and the European Union consider the PKK a terrorist organization, AFP noted. Biden said the PKK poses a real threat to Turkey, adding, it “is a terrorist group plain and simple.”

But the U.S. has been accused of trying to support militants in the Democratic Union Party, or PYD, in the fight against ISIS. The PYD reportedly has ties to the PKK, and Turkish Prime Minister Ahmet Davutoğlu said Saturday the group was collaborating with the Syrian regime that allowed ISIS to thrive, Today's Zaman reported.

Davutoğlu, stressing the strength of the Turkey-U.S. relationship, said he and Biden have “decided to continue our struggle against all sources of terrorists.”

Biden went on to say Saturday the White House was ready to use force to solve the situation in Syria. “We do know that it would be better if we can reach a political solution, but we are prepared — we are prepared, if that's not possible, to have a military solution to this operation and to taking out [ISIS],” he added.