Despite assurances by US President Donald Trump that he and his Turkish counterpart ‘are very good friends’, their meeting at the White House could not solve the problem, which greatly aggravated relations between the two NATO allies, AP reported.

Trump and Erdogan concluded the meeting without reaching an agreement on Turkey’s decision to purchase Russian S-400 systems. This poses such a threat to NATO’s security that the US suspended Turkey’s participation in the multinational F-35 fighter production program.

Turkey has also been criticized on Capitol Hill for invading Syria to attack the Kurds who fought with the US against the ISIS. Turkey was criticized for the repression against political opponents, journalists and others.

Trump said Turkey’s purchase of a Russian air defense system creates serious problems, but hopes they can be resolved. He said that he had discussed this issue with Erdogan, and asked Secretary of State Mike Pompeo and other advisers to work on a solution to the problem.