The Kremlin described the conversation as “substantive” in an English-language statement that blamed the violence in Ukraine that has left dozens dead on “the radical opposition,” which it accused of taking the confrontation in the former Soviet state “to a very dangerous point.”

Washington has said that both security forces and protesters in Ukraine must refrain from violence but that it holds the government of Ukrainian President Viktor Yanukovych ultimately responsible for reining in the deadly clashes and stabilizing the situation.

Yanukovych on Friday signed an agreement with opposition leaders aimed at ending the nation’s deadliest violence since it gained independence in 1991, agreeing to an early presidential election and a return to a 2004 constitution designed to limit presidential powers and make the country a parliamentary republic.

In a call with reporters Friday, a senior US State Department official called the Obama-Putin phone call “constructive” and said the two leaders agreed that “the agreement reached today needed to be implemented quickly.”

“It’s clearly an important signal that the president and President Putin were able to talk positively about implementing this agreement,” the official said, the Washington newspaper The Hill reported on its website. “We have to move on from there and ensure that this very, very fragile Ukrainian economy is stabilized.”

The United States and its EU partners have been at odds with Russia over the crisis in Ukraine, with officials in Moscow accusing the West of stoking the violence by backing what they describe as radical elements seeking to carry out a coup against Yanukovych.

US and European officials have said they are merely supporting Ukrainians’ right to protest peacefully after mass demonstrations broke out there in November following Yanukovych’s decision to forego partnership and trade agreements with the EU in favor of closer integration with Russia.

As Obama and Putin were preparing to speak by telephone, White House spokesman Jay Carney told reporters Friday that “it is in Russia’s interest for the violence to end in Ukraine, as it is in the interest of the United States and our European friends.”

“We welcome the cessation of violence, and we welcome the agreements that have been reached,” Carney said.

Obama initiated the call, during which the two leaders also discussed Iran’s nuclear program and the situation in war-torn Syria, the White House and the Kremlin said.