As Ukraine's new president sought to end an insurgency in the country's east, US President Barack Obama spoke separately with French President Francois Hollande and German Chancellor Angela Merkel, the White House said.
"They agreed that should Russia fail to take immediate, concrete steps to de-escalate the situation in eastern Ukraine, the United States and the European Union would coordinate additional steps to impose costs on Russia," the White House said in a statement.
The leaders spoke amid heightened concerns about Russian activity along Ukraine's borders.
Ukrainian President Petro Poroshenko on Friday ordered a seven-day cease-fire in the fight against pro-Russian separatists but also warned them they could face death if they did not use the time to put down their guns. In Moscow, the Kremlin, whose support Poroshenko needs for his plan to end the insurgency in the rebellious east, denounced the cease-fire as an ultimatum to separatists rather than a peace offering.
Obama, Hollande and Merkel welcomed Poroshenko's cease-fire and urged Russia to pull back its military presence on the border, stop the flow of weapons and militants across the boundary and use its clout to persuade separatists to stand down.
The US State Department separately said it had information that Russia had gathered tanks and artillery at deployment sites that may be provided to separatist fighters in Ukraine.
Spokeswoman Jen Psaki also said the United States had its own information that Russia had redeployed military forces on its border with Ukraine. NATO said on Thursday at least a few thousand more Russian troops were now at the frontier. REUTERS