A bipartisan group of U.S. senators has urged Secretary of State John Kerry to tighten sanctions against Russia and provide defensive military aid to Ukraine after rebels breached this month's cease-fire agreement and seized the Ukrainian town of Debaltseve.
The senators told Kerry in a letter that "it is time to provide defensive weapons to Ukraine and to consider imposing additional sanctions and penalties that will increase the cost of Putin’s actions, including the potential removal of Russia from the SWIFT financial system."
Among those signing the letter were top Democrat Dick Durbin and Armed Services Committee Republican Chairman John McCain.
U.S. President Barack Obama has not ruled out giving the Ukrainians defensive lethal aid.
White House spokesman Josh Earnest said on February 20 that military operations by Russian-backed separatists in Ukraine risk "increasing costs" for Russia.
Meanwhile, U.S. Vice President Joe Biden also condemned the rebels assault on Debaltseve.
The White House said Biden spoke by phone separately on February 20 with Ukrainian President Petro Poroshenko and Prime Minister Arseniy Yatsenyuk.
According to the White House, Biden discussed options for "effective monitoring" of a ceasefire and withdrawal of heavy weapons from eastern Ukraine.
Biden also agreed with the Ukrainian leaders that Russia cannot continue to hide behind "the false claim" that the separatists are acting alone.
The United States warned Russia on February 20 that its continued support of the rebels was a direct threat to the "modern global order" and could bring additional costs.
"Russia's continued support of ongoing separatist attacks ... is undermining international diplomacy and multilateral institutions - the foundations of our modern global order," U.S. State Department spokeswoman Jen Psaki said.
She said Russia must honor its commitments immediately.
Her comments come after Ukraine accused Russia of sending more tanks and troops into Ukraine and said they were heading toward the rebel-held town of Novoazovsk, 40 kilometers east of the port city of Mariupol.