Russian and Ukrainian forces exchanged deadly cross-border drone and missile attacks during the overnight hours Sunday into Monday morning despite international diplomatic efforts to end hostilities.

The warnings over the offensive come as a U.S.-brokered peace process has limped along with inconclusive meetings and little concrete results.

A Ukrainian official says Russian forces have taken over four border villages in Ukraine’s northeastern Sumy region.

Russian energy minister Anton Rubtsov told state media about how current taxation on Russian oil hurts production.

Germany and other Ukrainian allies have lifted restrictions on Kyiv firing long-range missiles into Russia for the first time, the German chancellor said Monday, after days of Russia bombarding the capital and other regions with massive aerial attacks.

The U.S. president lashed out at the Kremlin Tuesday as the White House continued to consider increasing sanctions against Russia.

China denied the Ukrainian claims that it is supplying Russia with weapons for its ongoing war. "China has never provided lethal weapons to any party in the conflict and strictly controls dual-use items," Chinese foreign ministry spokesperson Mao Ning said on Tuesday morning, state-run Global Times reported.

Russia and Ukraine have completed the first phase of what is expected to be the biggest prisoner exchange since the start of the war, with almost 800 people released on Friday.