Geneva - In a surprise accord, Ukraine and Russia agreed Thursday on tentative steps to halt violence and calm tensions along their shared border after more than a month of Cold War-style military posturing triggered by Moscow's annexation of Crimea.

Russia's pledge to refrain from further provocative actions drew support but also a measure of skepticism from President Barack Obama, who said at a news conference at the White House that the United States and its allies were prepared to ratchet up sanctions if Moscow doesn't fulfill its commitments.

"I don't think we can be sure of anything at this point," Obama said after Secretary of State John Kerry, Russian Foreign Minister Sergey Lavrov and diplomats from Ukraine and Europe sealed their agreement after hours of talks in Geneva.

The abruptly announced agreement, brokered by the West, provides no long-term guide for Ukraine's future nor any guarantee that the crisis in eastern Ukraine will abate. But it eases international pressure both on Moscow and nervous European Union nations that depend on Russia for their energy.

Reached after seven hours of negotiations, the deal requires all sides to refrain from violence, intimidation or provocative actions. It calls for disarming all illegally armed groups and returning to Ukrainian authorities control of buildings seized by pro-Russian separatists during protests.

Notably, though, it does not require Russia to withdraw an estimated 40,000 troops massed near the Ukrainian border. Nor does it call for direct talks between Russia and Ukraine.

The agreement says Kiev's plans to reform its constitution and transfer more power from the central government to regional authorities must be inclusive, transparent and accountable. It gives amnesty to protesters who comply with the demands, except those found guilty of committing capital crimes.

The negotiations came against the backdrop of the bloodiest episode to date in the clashes that pit the new government in Kiev against an eastern insurgency the West believes is backed by Moscow.

In the eastern Ukraine Black Sea port of Mariupol, authorities said three pro-Russian protesters were killed and 13 injured overnight Wednesday during an attempted raid on a Ukrainian National Guard base.

As for the agreement reached in Geneva, monitors with the Organization of Security and Cooperation in Europe will be tasked with helping Ukraine authorities and local communities comply with the requirements. Lavrov said the OSCE mission "should play a leading role" moving forward.

Kerry called the one-page agreement "a good day's work." But, anticipating Obama's remarks a few hours later, he stressed that if Russia does not abide by a pledge to de-escalate the crisis by the end of the upcoming Easter weekend, the West would have no choice but to impose new sanctions as initially planned.

In a further sign of impatience on the part of the Obama administration, Defense Secretary Chuck Hagel said the U.S. would send non-lethal assistance to Ukraine's military in light of what he called Russia's ongoing destabilizing actions in the country. The aid will include medical supplies, helmets, water purification units and power generators.

In remarks at his own news conference in Geneva, Kerry said, "It is important that these words are translated immediately into actions. None of us leaves here with a sense that the job is done because of words on a paper."

Lavrov said the agreement was the product of compromise by the two sides that as recently as a several weeks ago refused to speak, intensifying the crisis and ratcheting up East-West tensions to levels not seen since the Cold War.

"Most important is that all participants recognize the fact that Ukrainians should assume leadership and ownership of settlement of the crisis in all aspects, be that resolving the issue in all aspects," Lavrov said.