Sources from the Presidential Palace and the government say that Turkey's national security cannot be a matter of negotiation and that it will adopt every legitimate measure to ensure its security. Commenting on the cease-fire that went into effect at midnight on Saturday, Turkish officials expressed their low hopes for the truce that was brokered between the United States and Russia. Ankara says the Syrian PKK affiliate Democratic Union Party (PYD) and it People's Protection Units (YPG), poses a threat to its security and the cease-fire will only effect the warring parties in Syria and that Ankara will take all sorts of military action when it sees it necessary. Commenting on the YPG's presence and its fight against moderate Syrian opposition groups, sources say that Turkey's struggle is aimed at the process heading toward the establishment of a state structure under the control of the PKK in northern Syria. Officials said Turkey "will never allow" attempts to establish such a PKK-affiliated autonomous structure or cantons on its borders.The Turkish military shelled YPG positions in northern Syria for a week beginning on Feb. 13 in response to artillery fire from YPG forces based around the town of Azaz, located 6 kilometers from the Turkish border.Saying that Ankara supports the Syria cease-fire in principal, presidential spokesman İbrahim Kalın said Turkey has also played an active role in the Syria cease-fire decision. He expressed Ankara's concerns over the ongoing attacks carried out by Russian and Syrian regime forces and said that Turkey wants to see concrete results. "We support this cease-fire in principle but the continuous air operations by Russian jets and ground offensives by [Syrian leader Bashar] Assad's forces cause serious concerns for us regarding the future of the truce." Earlier this week, Washington and Moscow announced a cessation of hostilities in Syria, which was scheduled to take effect at midnight Saturday local time. Kalın also said that Ankara has serious concerns over the future of the cease-fire due to ongoing attacks a few hours before the deal was due to start. "Turkey sees the deepening of the refugee crisis unless the Assad regime stops attacks," Kalın said, and added that the regime fights on the same side with the PYD and YPG.In remarks on Thursday, Prime Minister Ahmet Davutoğlu said that Ankara will neither hesitate to do what is necessary nor seek permission from anyone in case of a threat against its security from any party in Syria."All must know that this cease-fire is only valid for Syria and the warring sides in the country," he told the media during a trip to Konya. "If any of them poses a threat to Turkey's security, it becomes non-binding for us."Kalın echoed Davutoglu's remarks, saying: "Turkey will use its rights originating from international law and apply its rules of engagement to protect its national security, if necessary, no matter from which part of Syria or from which terrorist group the threat comes."Citing reports of ongoing shelling north of Aleppo, Azaz, Tal Rifaat, Idlib and the Turkmen Mountain region, which all are along the Syrian-Turkish border, Kalın said that the Assad regime had exploited previous peace talks in Vienna and Geneva to stall for more time. "We hope it will yield a different result this time," he said.Kalın said that the PYD and YPG has been established based on the orders of imprisoned PKK leader Abdullah Öcalan in 2003, making it an offshoot of the latter, despite the U.S. not considering it terrorist organizations. He also said that Turkey has deported around 3,800 suspects as part of the anti-terror fight against DAESH. The PYD was not invited to the talks by the U.N. special envoy for Syria Staffan de Mistura. Ankara lists the PYD and its YPG militia as terror organizations. The YPG has recently been supported by Russian air power in northern Syria.The PYD is largely accepted as the Syrian affiliate of the PKK, which is recognized as a terror organization by the U.S., EU and NATO. The group recently opened an office in Moscow adorned with a poster of Öcalan.Kalın further ruled out any preparations by the Turkish military together with Saudi Arabia for a ground operation into Syria, but said Ankara rather focuses on "acting in concert with the international coalition.""What we talk about is that the air shelling in the anti-DAESH fight is not enough alone, but that support is required for the opposition forces on the ground, like the Free Syrian Army, in order to gain ground supremacy," he said.According to U.N. figures released several months ago, more than 250,000 have been killed since the Syrian war began in 2011.This week, President Recep Tayyip Erdoğan said that around 400,000 people had died and 12 million people been displaced since the war started.