<p>President Donald Trump will confront Turkey's leader about his decision to buy a Russian air defense system when they meet this week at the White House amid strained relations between the two NATO allies.</p>.<p>Trump's national security adviser, Robert O'Brien, said Sunday that the United States is still "very upset" by the move to purchase the Russian S-400 system.</p>.<p>The US says the system is not compatible with NATO forces and could compromise the F-35 fighter jet program and aid Russian intelligence.</p>.<p>The Trump administration removed Turkey from the F-35 program in July.</p>.<p>O'Brien told CBS' "Face the Nation" that if Turkey doesn't get rid of the Russian system, Turkey will likely face U.S. sanctions backed by a bipartisan majority in Congress.</p>.<p>Trump is scheduled to meet with Turkish President Recep Tayyip Erdogan on Wednesday and NATO Secretary-General Jens Stoltenberg on Thursday.</p>.<p>Trump and Erdogan plan a joint news conference Wednesday afternoon.</p>.<p>"There's no place in NATO for the S-400," O'Brien said.</p>.<p>"There's no place in NATO for significant Russian military purchases. That's a message that the president will deliver to him very clearly when he's here in Washington."</p>.<p>O'Brien said, however, that the U.S. will do everything it can to keep Turkey in NATO.</p>.<p>Turkey has been roundly criticized for its incursion into northern Syria to attack Kurdish forces that were fighting with the US against Islamic State militants.</p>.<p>Trump has been denounced for removing U.S. forces from the area before the incursion, but O'Brien said the administration did not pave the way for Erdogan's offensive into Syria.</p>
<p>President Donald Trump will confront Turkey's leader about his decision to buy a Russian air defense system when they meet this week at the White House amid strained relations between the two NATO allies.</p>.<p>Trump's national security adviser, Robert O'Brien, said Sunday that the United States is still "very upset" by the move to purchase the Russian S-400 system.</p>.<p>The US says the system is not compatible with NATO forces and could compromise the F-35 fighter jet program and aid Russian intelligence.</p>.<p>The Trump administration removed Turkey from the F-35 program in July.</p>.<p>O'Brien told CBS' "Face the Nation" that if Turkey doesn't get rid of the Russian system, Turkey will likely face U.S. sanctions backed by a bipartisan majority in Congress.</p>.<p>Trump is scheduled to meet with Turkish President Recep Tayyip Erdogan on Wednesday and NATO Secretary-General Jens Stoltenberg on Thursday.</p>.<p>Trump and Erdogan plan a joint news conference Wednesday afternoon.</p>.<p>"There's no place in NATO for the S-400," O'Brien said.</p>.<p>"There's no place in NATO for significant Russian military purchases. That's a message that the president will deliver to him very clearly when he's here in Washington."</p>.<p>O'Brien said, however, that the U.S. will do everything it can to keep Turkey in NATO.</p>.<p>Turkey has been roundly criticized for its incursion into northern Syria to attack Kurdish forces that were fighting with the US against Islamic State militants.</p>.<p>Trump has been denounced for removing U.S. forces from the area before the incursion, but O'Brien said the administration did not pave the way for Erdogan's offensive into Syria.</p>