Russia and Ukraine, backed by the U.S., traded accusations of violating the agreement made in Geneva to defuse tensions between them, as Vice President Joe Biden arrived Monday in Kiev with a warning of new sanctions.

The Russian Foreign Minister Sergei Lavrov accused the Ukrainian government of flagrantly violating last week's agreement by not moving to immediately disarm what he called extremists in Ukraine.

Russia blamed authorities in Kiev on Monday for the violence in eastern Ukraine, accusing them of trying to ignite a civil war in a region where pro-Russian militants have been defying the central government.

The warning came as Vice President Biden arrived Monday in the Ukrainian capital for a two-day visit to meet with political leaders, civil society groups and U.S. diplomats. He is bringing U.S. economic assistance, as well as warnings to Russian President Vladimir Putin that future intervention in Ukraine’s volatile east will incur new costs.

Russia accused the Ukrainian government of failing to rein in extremists as escalating tensions threaten to undermine a diplomatic accord reached last week and stoke calls in the U.S. for economic sanctions.

Ukrainian and Russian officials traded accusations about responsibility for attacks that killed three during the weekend. Foreign Minister Sergei Lavrov in Moscow called on the U.S. to hold the Ukrainian authorities accountable for observing the agreement signed in Geneva, which calls for all illegal groups to disarm and seized buildings to be returned.