Ukraine is struggling to keep control of key cities in its pro-Russian east as demonstrators seize government buildings and demand votes on joining Russia.
Authorities said shots were fired and at least 60 protesters arrested in Kharkiv Tuesday, while pro-Russian demonstrators held on to government offices captured Sunday in Donetsk.
Ukrainian security officials said protesters in Luhansk wired an occupied building with explosives and were holding 60 hostages.
U.S. Secretary of State John Kerry accused Russian agents and special forces of stoking separatist unrest in eastern Ukraine. He called the Russian actions "a contrived pretext for military intervention just as we saw in Crimea."
Kerry told a Senate committee Tuesday that Moscow's involvement in Ukraine was "clear and unmistakable." He said President Barack Obama is preparing more tough sanctions on Russia if it continues destabilizing Ukraine.
Also Tuesday, Russian Foreign Minister Sergei Lavrov said southeastern Ukraine should be included in talks about the country's future. He said Russia wants to see the largely Russian-speaking region represented in multilateral talks.
Meanwhile, U.S. Vice President Joe Biden spoke with two European leaders on the crisis in Ukraine.
Biden met with Montenegrin Prime Minister Milo Djukanovic at the White House and telephoned Slovakian Prime Minister Robert Fico. Biden thanked Fico for helping Ukraine diversify its energy supplies so it is not so dependent on Russian natural gas.
Taking issue with the Obama administration’s approach on Ukraine, Republican Senator John McCain said that not enough was being done to counter Russia’s moves.
He said that instead of talking softly and carrying a big stick, the administration was doing the opposite, adding that steps taken in response to what he called the
“Russian dismemberment of Ukraine” were insufficient.
“Some individual sanctions, some diplomatic sanctions, suspension, not removal [of Russia] from the G8, and now, more threats to come,” said McCain.
In an effort to de-escalate tensions in Ukraine, the U.S., the European Union, Russia and representatives of Ukraine’s government are set to meet in Europe within the next ten days.
In Paris, NATO chief Anders Fogh Rasmussen warned that further Russian intervention in Ukraine would be a "historic mistake" that would further isolate Russia from the world.
He urged Russia to pull back its troops from the Ukrainian border and engage in constructive dialogue with the Kyiv government.
Russia still maintains tens of thousands of troops on its borders with Ukraine as part of what it calls military exercises.
Meanwhile, NATO has announced it will triple its usual number of fighter jets patrolling over the Baltics next month to beef up its eastern European defenses due to tensions with Russia over Ukraine, a NATO military official said on Tuesday.
Four NATO fighters are usually based in the Baltics but the United States, which currently has responsibility for patrolling the skies there, increased that to 10 F-15s to reassure those states following Russia's occupation of Ukraine's Crimea region.
Some reporting by Reuters