Syria has been offering citizenship to ethnic Kurds and allowing the Kurdistan Workers Party, familiarly known as the PKK and considered by the US State Department to be a terror organization, to operate against Turkey from within Syrian territory, further fueling the conflict between the neighboring countries.

“After years of no ties between them, Assad has once again welcomed the PKK in Syria,” said Dr. Ely Carmon, a Senior Research Scholar at the Institute for Counter-Terrorism at the Interdisciplinary Center (IDC) in Herzliya.

The uprising in Syria, and the brutal response by Bashar Assad’s regime, have strained ties between Turkey and Syria and pushed them to the brink of armed conflict.

Tension escalated late last week when Syrian troops shot down a reportedly unarmed Turkish military jet that briefly crossed over Syrian skies. Ankara responded with a troop deployment to the 550-mile border. Syria responded in kind, sending some 170 tanks to the area.

The two countries, allied for 18 years, nearly went to war in the late ’90s over Syrian support of the PKK.

The organization was established in 1978, in Lebanon, a country ruled by Syria at the time. The PKK launched cross-border raids into Turkey and was supported by both Damascus and Moscow – the former as part of a territorial dispute and the latter as part of Cold War maneuvering against Turkey, a key NATO country. Syria continued to host the PKK and its leader Abdullah Ocallan until the late ’90s, when Turkey threatened war. The Assad regime relented, ousted Ocallan and signed a treaty with Turkey.

This has changed drastically over the past 17 months of uprising in Syria.

The Sunni Muslim leadership in Turkey was quick to condemn the bloodshed in Syria. It opened the border to tens of thousands of Syrian refugees and has allegedly been providing military assistance to the Sunni guerrilla units fighting against the Alawite regime. Damascus responded with two moves that relate to the stateless, Kurdish-minority living in northwestern Syria, Turkey, Iran and Iraq.

The first is internal. According to an article written by Soner Cagaptay, Director of the Turkish Research Program at the Washington Institute for Near East Studies, in late 2011 Assad offered “Syrian Arab” citizenship to 300,000 ethnic Kurds and allowed Kurds in Syria to open six Kurdish language schools in the region. They were permitted, for the first time, to teach students in their language and fly their flag. Cagaptay and others interpreted the move as an attempt to placate a potential foe in the roiling, multi-ethnic state of Syria.

In addition, beginning in March 2012, Assad welcomed the PKK back to Syrian soil. Cagaptay reported that some 1,500-2,000 PKK troops moved from the Qandil enclave along the Iran-Iraq border to Syria.

After three Turkish officers were killed in an attack near the Syrian border in May, Turkish Interior Minister Idris Naim Şahin confirmed to the Turkish Zaman Times that “terrorist grouping that were not there a year ago have been spotted.”

The PKK, according to Carmon, is being used as a double-edged sword — “mostly against Turkey, to try and deter them from aiding the opposition,” Carmon said, “but also internally.”

A UNHCR report, authored by Emrullah Uslu in April, confirmed this suspicion, claiming that the PKK has been smothering resistance to the Assad regime by assassinating Kurdish leaders who want to join the armed opposition within Syria.

As a response to these developments, the Turkish national security council has been discussing the establishment of a Turkish security zone within Syria.

“This could be the trigger for those plans,” said Carmon.