Ankara (AFP) - Turkey on Friday denied it had struck a secret new pact with Saudi Arabia to back Islamist rebels in Syria in a drive to bring down Syrian President Bashar al-Assad.

Reports have suggested that Riyadh and Ankara agreed a special pact to militarily and financially support Islamist rebels in Syria in an all-out effort to oust Assad from power.

The suggestions emerged after Islamist rebels -- including fighters from Al-Qaeda affiliate Al-Nusra Front -- captured the Syrian city of Idlib from government forces and made striking new gains.

"What has been said about Saudi Arabia is nothing new, our views have coincided with Saudi Arabia on Syria for years," foreign ministry spokesman Tanju Bilgic said.

"I can say that there isn't a new element to it (the cooperation)," he added in televised comments.

"Turkey cooperates not only with Saudi Arabia but other allies as well, like Britain and United States."

Bilgic also rejected claims that Turkey was aiding Al-Nusra Front, noting the group was on Ankara's list of prohibited terrorist organisations.

Turkey and Saudi Arabia have had long-standing differences on how to deal with Assad and relations also strained badly in recent years over Egypt.

But ties have recently shown signs of warming under newly-crowned Saudi King Salman, who Turkish President Recep Tayyip Erdogan visited in March.

Turkey has long argued there can be no solution for the Syria conflict until Assad leaves power.

Bilgic also denied as "baseless" and "speculative" claims that a US-led plan to train and arm moderate Syrian rebel forces fighting against Assad might not start in Turkey.

"The programme continues as planned. There is no problem in the preparations. It will start in the coming days," he said.

Turkey and the US inked a deal in February to train and equip the moderate Syrian opposition on Turkish soil. But the plan has been marked by disagreement between Washington and its allies about the objective of the training.

Turkey and other governments want to see the rebels confront the Syrian regime, while Washington has said the first priority must be combating the Islamic State (IS) jihadists who hold vast swathes of territory in Syria and Iraq.