Saudi jets on Friday arrived at a Turkish base to join the air campaign against Islamic State jihadists in Syria only hours before a ceasefire is to take force, Turkish and Saudi media reported.
Four F-15 jets landed at Incirlik air base in the Adana province in southern Turkey, the state-run Anatolia news agency reported.
The official Saudi Press Agency said an unspecified number of fighter jets arrived at Incirlik "to widen operations against IS".
The base is already hosting US, British and French war planes taking part in the strikes against IS fighters in Syria.
Saudi Arabia's air force had already sent ground personnel and equipment aboard C-130 Hercules military transport planes early this week.
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The partial truce to end hostilities in Syria, brokered by Russia and the United States, is due to begin at midnight Friday. The deal excludes IS and other jihadists.
Turkey on Friday expressed alarm over the viability of the ceasefire as the Syrian regime and its ally Russia pressed ahead with an offensive.
The two overwhelmingly Sunni Muslim powers, Saudi Arabia and Turkey, both see the ousting of Syrian President Bashar al-Assad as essential to ending Syria's five-year civil war and are bitterly critical of Iran and Russia's support of the Syrian regime.
Ankara has said it is in favour of a ground operation in Syria, but only if it is conducted in coordination with Saudi Arabia as well as Western and Gulf members of the anti-IS coalition.
Turkish Foreign Minister Mevlut Cavusoglu on Thursday said: "We have since the beginning argued for the necessity of ground operations and all kinds of strategic moves to be carried out in addition to the air campaign."