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By Daren Butler
ISTANBUL, March 5 (Reuters) - There is no unanimity in Washington over support for Turkey in Syria's Idlib because of Ankara's purchase of Russian S-400 defence systems, U.S. envoy James Jeffrey said on Thursday.
Fighting in Idlib has intensified in recent weeks as Russia-backed Syrian government forces mounted an offensive to retake the last rebel-held bastion in the country, displacing nearly a million people.
Turkey, which backs rebels fighting Syrian President Bashar al-Assad, has launched a counter-offensive and asked its NATO allies for support, including a request to the United States to use U.S. Patriot missile defence systems.
However, Washington and Ankara have been at odds over Turkey's purchase of the Russian missile systems, which Washington says are not compatible with NATO defences and may compromise its F-35 stealth fighter jets.
Speaking in Istanbul, Jeffrey repeated that Washington had already offered humanitarian assistance and information sharing with Turkey, but added that U.S. officials were divided over any further support.
"There is not unanimity of views in Washington on what to do and how fast to do it. This is still being reviewed," U.S. Syria envoy Jeffrey told a panel on Idlib in Istanbul, describing the S-400 issue as "a very serious concern for the U.S. Congress and for our defence establishment."
Jeffrey said Turkey and the United States were looking for ways to work around the S-400 issue, reiterating that the United States was pressing its NATO and European allies for significant contributions to efforts in Idlib.
U.S. Ambassador to Ankara David Satterfield said on Tuesday that the United States had received Turkey's request for the use of Patriot systems and that Washington was evaluating it within the context of the S-400s.
Turkish President Tayyip Erdogan traveled to Moscow on Thursday for talks with his Russian counterpart Vladimir Putin on developments in Idlib. Ankara has said it is hoping to reach an agreement on a ceasefire in the region.
(Reporting by Daren Butler; Writing by Ezgi Erkoyun and Tuvan Gumrukcu; Editing by Dominic Evans)