The Turkish president has said his country cannot continue the peace process with the Kurds amid attacks by Kurdish militants on Turkish targets.
There has been a recent series of clashes between Turkish forces and Kurdish PKK militants.
Turkey has also been hit by attacks by by Islamic State-linked militants – including one that left 32 dead in the town of Suruc last week.
Turkey considers both the PKK and IS terrorist organisations.
Over the past week, analysts say, Turkey has turned its approach to the US-led coalition against IS on its head.
Previously a reluctant partner, it is now flying combat missions and making its airbases available to US jets.
President Recep Tayyip Erdogan told reporters in Ankara that it was “not possible to continue the peace process with those who threaten our national unity and brotherhood”.
But the leader of Turkey’s pro-Kurdish opposition party – the People’s Democratic Party (HDP) – dismissed the claim.
HDP chairman Selahattin Demirtas insisted his party’s only crime was winning 13% of the vote in June elections, reported Reuters news agency.
Turkish police have continued to arrest suspected members of IS, the PKK and leftist groups – more than 1,000 over the past week.
Although Turkey insists Syrian Kurds are “outside the scope of the current military effort”, analysts say its new determination to tackle IS is linked to keeping a check on Kurdish militancy.
Speaking after Mr Erdogan, a spokesman for the ruling AK Party insisted that the peace process with Kurdish militants could continue if “terrorist elements” put down their weapons and left the country.
“We cannot say that the peace process is de facto over,” Besir Atalay told a news conference in Ankara.
“There is currently a stagnation in the mechanism but it would restart where it left off if these intentions emerge.”
Turkey’s allies are nervous that it could link its actions against IS and the PKK in ways that they would rather avoid.
For the Americans, strikes against Kurdish armed groups in Iraq and Syria are highly unwelcome because these troops are among the few reliable partners they have on the ground in the struggle against IS.
To the Turks, the so-called Caliphate of IS and the PKK are two sides of the same coin – terrorist movements that endanger their security while exploiting the power vacuum in northern Syria and Iraq.
Mr Erdogan apparently calculates that hitting the PKK, against which Turkey fought a long and bitter insurgency, will not overly endanger his relations with the US or a two-year-old ceasefire with the Kurdish group; nor will they shatter the peace of south-east Turkey more generally.
Turkey is struggling with more than 1.8 million refugees from the Syrian conflict.
Mr Erdogan said plans being discussed with the US to establish a “secure zone” in northern Syria would pave the way for the refugees’ return.
Under the plan, militants would be removed from a 68-mile (109km) stretch west of the Euphrates River, officials say.
Such a deal would significantly increase the scope of the US-led air war against IS in northern Syria, say analysts.
Tuesday also saw Nato discuss the Turkish campaigns against IS and Kurdish militants. All 28 Nato member countries met in Brussels to discuss what it called “the threats against Turkey”, a key member of the alliance.
In a final communique, Nato expressed “strong solidarity” with Turkey, and sent condolences to Ankara and “the families of the victims in Suruc and other attacks against police and military officers”.
However, Nato officials quoted by news agencies said alliance members use the closed-door meeting to urge Turkey not to use excessive force, and to continue peace talks with representatives of its Kurdish minority.
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