Former US Secretary of Defense Robert Gates called on President-elect Joe Biden to increase pressure on Turkey.

In an article in the New York Times, Gates noted that the US sanctions were a good start, but Biden must go further and even consider taking steps to isolate Turkey from other NATO countries. 

Turkey's purchase of the Russian S-400 air defense system, despite repeated US warnings, should have repercussions, Gates wrote adding that there is no provision in the NATO charter for the exclusion of a member state, but creative diplomacy is possible, including suspension of powers or other punitive measures.

Gates also criticized Turkey's actions in Libya, Syria, and the eastern Mediterranean, where he said Ankara was acting against the interests of other NATO members.

The United States needs to take the lead in NATO to determine the consequences for member states - such as Turkey, Hungary, and increasingly Poland - that are moving towards authoritarianism, he added.