U.S. Congress is ready to impose sanctions on Turkey unless it abandons its Russian S-400 air missile defence systems, the Hill quoted the U.S. National Security Advisor Robert O’Brien as saying on Sunday.

There is no place in NATO for the S-400 system and U.S. President Donald Trump will deliver that message to his Turkish counterpart when Erdoğan visits Washington, O’Brien said during an interview with CBS.

Ankara and Moscow in Sept. 2017 signed a loan agreement for the supply of Russian S-400 air defence systems to Turkey. The United States and its NATO allies see the Russian system as incompatible with NATO systems and posing a security threat to the F-35 stealth fighter. Turkey began to take delivery of S-400 components in late July, prompting Washington to remove Turkey from the F-35 fighter jets programme.

“We’re very upset about that,” O’Brien said referring to Turkey’s procurement of the S-400 sytem, adding that “there will likely be sanctions” if Turkey does not “get rid of” the weapons.

O’Brien also said Washington was “very concerned” about possible Turkish war crimes in northern Syria, where Turkey has launched an offensive targeting U.S.-backed Kurdish forces.

“Some of the things that we’ve seen are very disturbing… we’re very concerned about the war crimes issues, we’re watching them, we’re monitoring them very closely,” the U.S. national Security advisor said.

Turkish President Recep Tayyip Erdoğan is scheduled to meet with his U.S. counterpart Donald Trump in Washington this week amid soaring tensions over the Turkish offensive in Syria and the House of Representatives passing a resolution recognising the mass killings of Armenians by the Ottoman Empire in 1915 as genocide, a claim Turkey officially denies.