Russia and Ukraine traded accusations Monday over deadly drone strikes on civilian areas as Ukrainian President Volodymyr Zelenskyy prepared for a "very intense week" of diplomacy at the U.N. General Assembly in New York, where the Security Council is set to address the ongoing war.

Zelenskyy has tried to give momentum to a U.S.-led peace effort, offering a cease-fire and a summit meeting with Russian President Vladimir Putin. Moscow has taken issue with some of the proposals, however, and an end to the bloodshed appears no closer.

Additionally, international concerns have mounted recently that the fighting could spread beyond Ukraine’s borders as European countries rebuked Russia for what they said were provocations. The incidents have included Russian drones landing on Polish soil and Russian fighter aircraft entering Estonian airspace.

Latvian President Edgars Rinkevics said on social media that Russia was testing NATO’s political and military response, and aiming to reduce Western support for Ukraine by compelling countries to redirect resources toward the defense of members.

Calibrating how to respond to Russia was not easy, Rinkevics said Sunday. Russia was doing just enough not to cross a red line, but things could still spiral, he added.