A Group of United States senators forwarded a letter to the country's President Joe Biden on Thursday, urging him to hold off the sale of F-16 fighter jets to Turkey until Ankara ratifies accession of Finland and Sweden to the North Atlantic Treaty Organization (NATO).

"Failure to ratify the protocols or present a timeline for ratification threatens the alliance's unity at a key moment in history, as Russia continues its unprovoked invasion of Ukraine," US Senators Bill Cassidy, Jeanne Shaheen, and Thom Tillis wrote. "Sweden and Finland will bring new and advanced capabilities to the alliance that will better position NATO to respond to current and emerging threats," they added.

Last month, Turkish President Recep Tayyip Erdogan underscored that Ankara will no longer support Sweden's membership to the alliance following a series of incidents in the country's capital city, Stockholm.