Representatives from Russia, Ukraine, the United States and European Union reached a deal Thursday aimed at de-escalating the violence in eastern Ukraine that's threatening to topple the new government in Kiev.
The deal temporarily tables economic sanctions the West had planned to impose on Moscow should the talks prove fruitless.
U.S. Secretary of State John Kerry said Thursday's agreement "represents a good day's work."
However, he warned that words on paper "will have little meaning if they are not followed by actions on all sides to calm the situation in the former Soviet Republic."
"All illegally seized buildings must be returned to legitimate owners," Kerry said. "All illegally occupied streets, squares and other public places in Ukrainian cities and towns must be vacated."
Kerry added that if no improvement is seen, there will be "no choice but to impose" increasing sanctions against Russia."
The news comes as the Ukraine military steps up its operation to re-take government buildings in several eastern cities from pro-Russia separatists who want closer ties with Moscow.
Ukrainian troops repelled an attack on a National Guard base overnight Thursday, killing three pro-Russia militants and wounding 13.
The attack comes one day after militants seized six armored vehicles and paraded them through Slaviansk, a town controlled by the insurgents.
Eastern Ukraine was the support base for ousted President Viktor Yanukovych. Its population is largely Russian-speaking, and they support strengthening ties with Moscow.
Ukraine and the West blame Russia for using its influence in the area to spark the ongoing unrest.
"Russia has a new export. Aside from oil and gas, Russia is now exporting terrorism to Ukraine," Ukranian Prime Minister Arseniy Yatsenyuk said.
On Tuesday, the government deployed the Ukrainian military to the region for what's being called a large-scale anti-terrorist operation.
The White House applauded the move.
"The Ukrainian government has the responsibility to provide law and order," White House press secretary Jay Carney said. "These provocations in eastern Ukraine are creating a situation in which the government has to respond."
Currently, the Obama administration is working on an aid package for Ukraine. It may include medical supplies and clothing, but would stop short of providing weapons or ammunition.
Meanwhile, Russia is warning Ukraine to proceed with caution. President Vladimir Putin said a bloody crackdown on protesters will start a civil war and result in Russian intervention.
"I remind you that the Federation Council has given the president the right to use armed forces in Ukraine," Putin said in a televised question-and-answer session Thursday.
"I really hope that I do not have to exercise this right and that by political and diplomatic means we will be able to solve all of the sharp problems," he added.
The escalating tension between Russia and Ukraine has NATO bolstering its forces in Eastern Europe, preparing for what could soon become an all-out war.