U.S. Defense Secretary Lloyd Austin visited Romania as part of a three-country tour to reassure Black Sea allies on security issues amid ongoing tensions with Russia, AP reports.

Austin met yesterday with his counterpart Nicolae Ciucă and President Iohannis. He also visited Mihail Kogălniceanu airbase, near Constanța.

“The security and stability of the Black Sea are in the United States’s national interest and are critical to the security of NATO’s eastern flank”, he told reporters. “The region, it goes without saying, is vulnerable to Russian aggression.”

According to the Pentagon, Austin’s visit, which in addition to Romania included visits to Georgia and Ukraine, is meant to “reassure allies and partners of America’s commitment to their sovereignty in the face of Russian aggression”.