A renewed alliance between Damascus and the PKK would anger Turkey and could prompt it to take an even stronger line against Syrian President Bashar al-Assad over his brutal repression of anti-government protesters.
PKK’s acting leader Murat Karayılan said Turkey was preparing the ground for an intervention in Syria.
"The Turkish state is planning an intervention against our people," the Europe-based Fırat news agency, close to the PKK, quoted him as saying.
"Let me state clearly, if the Turkish state intervenes against our people in western Kurdistan, all of Kurdistan will turn into a war zone," he said.
Western Kurdistan is the term Kurdish nationalists use to describe Kurdish areas of northeast Syria, while by Kurdistan they mean the Kurdish areas of Turkey, Iraq, Syria and Iran.
Turkish Prime Minister Recep Tayyip Erdoğan said last week that setting up a "safe zone" or a "buffer zone" along the border with Syria to protect civilians from Assad's forces was among the options being considered should the stream of refugees turn into a flood.
Setting up such a zone would involve troops entering Syria to secure territory. Turkey has turned sharply against its former friend Assad and has taken a lead in trying to forge international agreement on the need for stronger action on Syria.
While Syrian government forces are clashing daily with insurgents demanding the downfall of Assad, Syrian Kurdish areas have remained relatively calm, despite many Kurds' long-standing opposition to the government.
Some Syrian Kurdish groups opposed to Assad have formed their own umbrella group after complaining of being sidelined by the main opposition Syrian National Council (SNC), which they say is dominated by Arab nationalists.
But the comparative calm in Syria's Kurdish northeast may also be related to what some Kurdish analysts say is the growing influence of the Democratic Union Party (PYD), a Syrian Kurdish group allied to the PKK which has kept away from the opposition.
Turkey warns Syria on PKK
The PKK, set up in 1984 to fight for Kurdish home rule in southeast Turkey, is commanded from bases in the remote mountains of northern Iraq, but was once backed by Syria.
Though Turkey has the second biggest army in NATO, it has failed to quash the PKK in 27 years of bitter fighting. More thann 40,000 PKK members, soldiers and civilians have been killed in the conflict. Turkey, the United States and the European Union all list the PKK as a terrorist organisation.
Turkish officials say they are watching closely for signs Syria may renew its support for the PKK, which it dropped in late 1998 after Turkish tanks massed on the Syrian border. Damascus was forced to deport PKK leader Abdullah Öcalan who was later seized by Turkish special forces in Kenya.
Turkish Foreign Minister Ahmet Davutoğlu has repeatedly said Syria "would not dare" make such a mistake again.
Kurds make up at least 10 percent of Syria's population. Like the majority of Syrians, they are Sunni Muslims, but have struggled to assert their ethnic identity under 40 years of Arab nationalist Ba'ath Party rule.
The Assad regime had denied some stateless Kurds Syrian nationality documents but it has made concessions since the start of the uprising to ease unrest in Kurdish areas.
Some Arabs are concerned that the Kurds, mostly based in northeast Syria on the borders with Turkey and Iraq, secretly seek a separate state that includes crossborder territories.
Syrian Kurd opposition groups deny wanting a separate state, but say they want autonomy similar to that of the Iraqi Kurds.