Syria provided PKK with training, safe haven, weapons and money, says declassified document from 1987.
"[...] the survival of the Kurdish resistance depends to a large extent on outside support. As the Iran-Iraq war has become increasingly stalemated, foreign aid to the guerillas has grown," according to a 1985 memo on "The Kurdish resistance in Iraq, Iran and Turkey". "We believe Syria supports the Iraqi Kurds primarily to exhaust Iraq's Army and undermine popular morale. It also hopes to keep the Iraqis preoccupied so they cannot pursue subversion against Damascus."
The memo also said that "Syria supports the Turkish Kurds to put pressure on Ankara on issues of concerns. According to US Embassy officials in Damascus, the Syrians are worried that Turkey's construction of the Ataturk Dam on the Euphrates will diminish Syria's water supply and limit its hydroelectric power generation." It added: "President [Hafez al-] Assad also almost certainly fears that Turkish ties to the United States work against Syria's strategic interests."
"Syria has backed the Kurdish Workers' Party (PKK) since the early 1980s, providing the group with training, safe haven, weapons and money," said another memo dated 1987. The PKK is designated a terrorist organization by Turkey, the U.S. and EU and has launched violent attacks in Turkey since 1984 that have led to tens of thousands of deaths.