The Syrian Democratic Union Party (PYD) affiliation with the PKK terrorist organization is the main reason it poses a threat to Turkey's national security. After purging the southeastern district of Cizre, security units found tunnels that were used by PKK-People's Protection Units (YPG) terrorists – the PYD's armed wing – to bring in weapons, explosives and militants from Syria to Turkey.
As mentioned in reports prepared by Amnesty International and the London-based Syrian Network for Human Rights (SNHR), the PYD has committed multiple human rights violations, including ethnic cleansing and abusing women, children and media staff.
The militant group is also known to have close relations with Syrian leader Bashar Assad's regime, which has denied basic human rights to Kurds throughout the Baathist regime-era in Syria. The regime has recently provided large amounts of weaponry to the PYD's armed wing and hesitated from making this information public in the media.
The moderate Syrian opposition groups, which were once strongly backed by the West but were abandoned after Russian intervention, have suffered at the hands of PYD attacks, which led them to be suffocated between DAESH, the PYD and the regime, which is backed by Russia and Shiite militias from various countries in the region.
In the name of fighting DAESH, the YPG refrained from keeping its promises of conducting an offensive into DAESH-held Raqqa. The PYD has used the DAESH card to pull weapon support from international powers but instead it has solely focused on taking control of the territories bordering Turkey. Its link to the PKK are is not the only threat as the PYD's expansionist policy also threatens Turkey's fight against DAESH.