The Jamestown Foundation's Terrorism Monitor, 12 Apr 07:

Turkey's Coming Offensive Against the Iraqi-based PKK
...Turkey and Iran have quietly worked out a reciprocal security arrangement, whereby Iran's military will engage Kurdish separatists whenever encountered, in exchange for Turkey's cooperation against the Iranian Mujahideen-e-Khalq movement (MEK), a well-armed and cult-like opposition group that previously found refuge in Saddam Hussein's Iraq. Both Iranian officials and Turkey's prime minister have alluded to "mechanisms" (likely to involve intelligence-sharing) already in place to deal with security issues of mutual interest. Neither Turkey nor Iran has any desire to see an independent Kurdish state established in northern Iraq.....