The US bombers were in the Baltic Sea region to train together with their NATO ally Finland, which shares a 1,340 km (833 miles) border with Russia.
Previous reports emerged that Russia has sought after foreign mercenaries from countries with "difficult economic situations" to fight in Ukraine.
The Kremlin said that it had "no doubt" that Washington understood its messaging behind Thursday's attack in central Ukraine.
Jake Reeves, 22, pleaded guilty at London's Woolwich Crown Court to charges of aggravated arson on the premises belonging to a "Mr X" on an industrial estate in east London in March.
Ukrainian Prime Minister Volodymyr Zelensky says the Russian missile strike with new weapon is a clear escalation of the 33-month-old war.
Civilian populations are allowed and even encouraged to flee combat zones to avoid danger. Why can't Gazans?
The launch was the latest sign of rapidly mounting tensions in the 33-month-old war after Ukraine fired US and British missiles at targets inside Russia.
"Out of an abundance of caution, the embassy will be closed, and embassy employees are being instructed to shelter in place," the statement said.
Israeli companies seek Ukraine’s expertise to counter Iranian kamikaze drones.
Global leaders at the Kyiv Jewish Forum 2024 stress unity, tackle rising antisemitism, and discuss support for Ukraine’s Jewish community amid ongoing war and shared global security challenges.