WASHINGTON (AFP) - US President Barack Obama said a deal on Thursday to de-escalate tensions in Ukraine was a "glimmer of hope" but cautioned he could not be sure if Russia would live up to it.
Mr Obama, in a careful response to the apparent breakthrough in Geneva, said he was coordinating with leaders in Europe about further sanctions against Moscow if progress was not evident within days.
"I don't think we can be sure of anything at this point. I think there is the possibility, the prospect, that the diplomacy may de-escalate the situation," Mr Obama told reporters after four-way crisis talks in Switzerland between the US, Russia, Ukraine and the EU.
He called for an end to what he said was interference by Russia in eastern and southern Ukraine, where Washington has accused the Kremlin of backing pro-Moscow separatists who seized government buildings.
"We are not going to count on it until we see it," Mr Obama warned.
In Geneva, the four parties agreed on steps to "restore security for all citizens," including a call to disband armed groups that have taken over buildings in Ukraine "illegally." Mr Obama made clear that if the West did not see action on those commitments, new sanctions would follow.
"We have put in place additional consequences that we can impose on the Russians if we do not see actual improvement of the situation." Mr Obama said he had discussed future measures with German Chancellor Angela Merkel and planned to speak to British Prime Minister David Cameron.
"We're going to prepare additional responses should Russia fail to take a different course," said Mr Obama.
"We've already had an impact on their economy. That is well-documented. It could get significantly worse." Earlier on Thursday, the United States said it would send helmets, medical supplies and other non-lethal military assistance to Ukraine.
Defense Secretary Chuck Hagel said shipments would include medicines, helmets, sleeping mats and water purification units for Ukraine's armed forces, and shelters, small power generators and hand fuel pumps for Ukraine's State Border Guard Service.
"The United States continues to stand with Ukraine," Mr Hagel said.
Washington has however balked at sending military supplies to Ukraine's ill-equipped forces - despite demands from Mr Obama's critics in Congress for such a step.
Senior officials argue that any swift US shipment would not change the military balance with Russian forces massed on Ukrainian borders and could incite further escalations by the Russian military.
One Obama critic, Republican Senator John McCain, decried steps taken by the US and European Union thus far against Russia as "almost laughable" during a visit to Lithuania on Wednesday.
He and other lawmakers have called on Washington to provide military assistance to Ukraine, including light arms and anti-aircraft defenses.