A top Kurdish leader warned in an interview that Turkey faces a “serious risk” of civil war as it battles Kurdish militants near its southern border. Selahattin Demirtas, the leader of the People’s Democratic Party, or HDP, spoke of the growing danger in a telephone interview Thursday from Diyarbakir, the area in southeastern Turkey that has seen sharp clashes between Turkish security forces and militants from the Kurdistan Workers’ Party, or PKK, which Turkey regards as a terrorist group.

“By summer, the tension between the PKK and government could grow,” Demirtas said through a translator. “Many Kurds and Turks could die, and this could trigger an ethnic war.”

Demirtas called for a ceasefire and peace talks to prevent further escalation. “We have urged the PKK to drop their guns and return to negotiations,” he said. He urged the U.S. or some other outside power to help broker such talks.

“We see it in everyone’s interest to end the violence and return to political dialogue,” a senior Obama administration official said in an interview late Thursday, when asked about Demirtas’s call for U.S. mediation. The U.S. is exploring ways to encourage this dialogue.

The Kurdish conundrum has been compounded by the alliance struck between the U.S. military and a Syrian Kurdish militia called the People’s Protection Units, known by its Kurdish initials as the YPG. U.S. commanders say the YPG has been the most effective group battling Islamic State fighters in Syria.

Turkish President Recep Tayyip Erdogan is said to have asked Obama to halt American military support for the YPG, which has close historic ties with the PKK. But Obama refused to cut U.S. links, upsetting the Turks. In the strange brew of the Syrian conflict, a NATO member (Turkey) has been opposing America’s best ally against ISIS terrorists (the YPG).

Turkey has taken out its frustration by pounding the PKK in Diyarbakir and other Kurdish areas of Turkey. Analysts warn that we’re seeing, in effect,a spillover of the Syrian conflict into Turkey—a much larger and strategically more important country. “There is a very real possibility that the recent escalation in violence in southeast Turkey could expand further into a civil war,” argues one prominent Turkish foreign policy expert. “This would be particularly dangerous when there is greater international attention than ever to ‘the Kurdish question’ because of the success of the Syrian Kurdish fighters against ISIS.”

Demirtas, 42, embodies the Kurdish resurgence that has been changing the political balance in Turkey, Syria and Iraq. His party last year won enough seats to be represented in the Turkish parliament, despite heavy pressure from Erdogan and the ruling Justice and Development Party, or AKP.

In Diyarbakir, Demirtas said, the Turkish military has been assaulting PKK militants since early December. Demirtas said that about 200 civilians are trapped inside an area of the city known as Sur; he said he visited parts of Sur Thursday but was blocked from entering six besieged neighborhoods.

Casualty estimates vary for the fighting in southeastern Turkey, and there aren’t confirmed numbers. But Turkish press accounts have suggest that several hundred Kurdish militants may have been have been killed, as well as a smaller number of security forces and many Turkish civilians.

Turkish Prime Minister Ahmet Davutoglu charged Wednesday that in supporting demonstrations to lift the siege in Diyarbakir, Demirtas was “plotting against the country” and “collaborating with terrorists to drag Turkey into chaos,” according to a Turkish press report.

Demirtas said in the interview that Davutoglu was making “an accusation with no basis” and that the Kurds were fighting against terrorism, rather than supporting it. “We Kurds have been the most efficient power in the Middle East against the barbarity of ISIS,” he said. “We don’t understand why the world stays silent about the attacks on us.”