Since Turkey shot down a Russian fighter jet on Nov. 24, the United States has quietly put on hold a long-standing request for its NATO ally to play a more active role in the U.S.-led air war against the Islamic State group.

The move, disclosed to Reuters by a U.S. official, is aimed at allowing time for Turkish-Russian tensions to ease. Turkey has not flown any coalition air missions in Syria against Islamic State since the incident, two U.S. officials said.

The pause is the latest complication over Turkey's role, testing the patience of U.S. war planners, who want a more assertive Turkish contribution — particularly in securing a section of border with Syria that is seen as a crucial supply route for the Islamic State.