GENEVA — Senior U.S. and Russian officials have formally launched special talks aimed at defusing tensions over a Russian military buildup on the border with Ukraine.

The talks are part of a flurry of diplomatic activity in Europe this week.

Russian Deputy Foreign Minister Sergei Ryabkov led a delegation arriving by Swiss police escort at the U.S. diplomatic mission in Geneva for the latest round of face-to-face talks with Wendy Sherman, the U.S. deputy secretary of state, and her team.

The New York Times reports that talks are expected to take most of the day Monday, with officials briefing reporters in the early evening.

The meeting is part of “Strategic Security Dialogue” talks launched by Presidents Joe Biden and Vladimir Putin during a June summit.

Western concerns have been raised because Russia has amassed over 100,000 troops on the border of Ukraine.

According to NPR, Secretary of State Antony Blinken has already rebuffed Russian requests that the U.S. remove troops from Eastern Europe or rule out expanding NATO to include Ukraine.