The United States’ new ambassador to Russia, Lynne Tracy, has arrived in Moscow, the U.S. embassy said Thursday.

Tracy most recently was the ambassador to Armenia and served as the deputy chief of mission in Moscow in 2014-17. She replaces John Sullivan, who resigned in September.

It was not immediately clear when Tracy would present her credentials.

Her arrival comes amid high tension between Russia and the United States, most recently sharpened by President Joe Biden’s decision Wednesday to supply advanced Abrams battle tanks to Ukraine. In recent years, staffing at the embassy in Moscow has been significantly reduced, obstructing visa applications and other consular services.