Biden calls Ukraine's president after helicopter shot down

Vice President Biden called Ukrainian President Petro Poroshenko on Tuesday after a government helicopter was shot down by pro-Russian separatists, violating a fragile ceasefire designed to bolster negotiations on a peace plan.

Biden offered his condolences for the nine Ukrainian service members who were lost in the attack, according to a statement from the White House.

The vice president also "underscored the importance of having monitors in place to verify violations of the ceasefire, as well as the need to stop the supply of weapons and militants from across the border," according to the statement.

The Ukrainian helicopter was hit by a rocket shortly after taking off near Sloviansk, a rebel-held city in eastern Ukraine, according to media reports.

Earlier Tuesday, White House press secretary Josh Earnest called on Russia to halt the transfer of more heavy weaponry to the separatists to prevent "additional violence like shooting down helicopters."

"What's critical right now are the actions that are taken by the Russian government to deescalate the situation," Earnest said.

Russian President Vladimir Putin said Tuesday morning that he welcomed the ceasefire agreement and hoped it would be extended and joined by face-to-face negotiations between rebel and government leaders.

The White House said it was encouraged by Putins words, and that an end of weapons disbursement would make "additional sanctions less likely." At the same time, Earnest cautioned that the administration would be monitoring Putin's deeds, not words.

"There is an opportunity for President Putin and Russia to play a constructive role in deescalating the situation in eastern Ukraine," Earnest said. "And the constructive role that they can play involves more than just words. It involves tangible actions. There's an opportunity for President Putin to take these actions and support the deescalation of the crisis."