The two countries one a democracy, the other a conservative kingdom have for years been at odds over how to deal with Assad, their common enemy. But mutual frustration with what they consider American indecision has brought the two together in a strategic alliance that is driving recent rebel gains in northern Syria, and has helped strengthen a new coalition of anti-Assad insurgents, Turkish officials say.
That is provoking concern in the United States, which does not want rebel groups, including the al-Qaida linked Nusra Front, uniting to topple Assad.
The coordination between Turkey and Saudi Arabia reflects renewed urgency and impatience with the Obama administration's policy in the region. Saudi Arabia previously kept its distance and funding from some anti-Assad Islamist groups at Washington's urging, according to Turkish officials.
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"The key is that the Saudis are no longer working against the opposition," a Turkish official said. He and other officials spoke on condition of anonymity because they were not authorized to brief the media.
Turkish officials say the Obama administration has disengaged from Syria as it focuses on rapprochement with Iran. While the US administration is focused on degrading the Islamic State group in Syria and Iraq, they say it has no coherent strategy for ending the rule of Assad, Iran's key ally in the region.
The pact was sealed in early March when Turkish President Recep Tayyip Erdogan flew to Riyadh to meet Saudi's recently crowned King Salman. Relations had been tense between Erdogan and the late King Abdullah, in great part over Erdogan's support of the Muslim Brotherhood.