Top diplomats from Ukraine, Russia, the European Union and the United States have agreed on a set of measures to ease mounting tensions in eastern Ukraine.
U.S. Secretary of State John Kerry, speaking Thursday in Geneva, said the measures include disarming pro-Russian militants occupying buildings in eastern Ukraine and the return of the buildings to their legitimate owners.
A joint statement from the four powers says amnesty will be granted to protesters who surrender weapons and leave the buildings, except for those found guilty of capital crimes.
Monitors from the Organization for Security and Cooperation in Europe, who already are in Ukraine, will be engaged in putting the de-escalation measures into place.
Kerry warned, however, that so far these plans are just "words on paper" and success will depend on how they are carried out.
At a White House press breifing later, U.S. President Barack Obama expressed caution.
The president said he hopes Russia lives up to the Ukraine agreement, but he added that past practice makes it unlikely.
"I don't think we can be sure of anything at this point," he said. "I think there is the possibility, the prospect, that the diplomacy may de-escalate the situation."
Obama left open the possibility of more sanctions if diplomacy fails.
"We have put in place additional consequences that we can impose on the Russians if we do not see actual improvement of the situation," he said.
Obama said a military option is not on the table.
The president consulted with European allies by phone Thursday to discuss a response to Russia if it does not follow through on its promises.
The seven-paragraph agreement reached in London on Thursday does not specifically require Moscow to withdraw 40,000 troops massed on its border with Ukraine, and does not reference Russia's annexation of Ukraine's Crimean peninsula last month. It also does not obligate Moscow to hold direct talks with the interim government in Kyiv.
But the four-party statement says monitors from the Organization for Security and Cooperation in Europe will immediately begin to put the de-escalation measures into place.
Russian Foreign Minister Sergei Lavrov said the four parties will work to establish a broad national dialogue to ensure protection of Ukrainians' rights.
Kerry met separately with Lavrov, Ukraine's foreign minister Andrii Deshchytsia, and the European Union's Catherine Ashton before the group meeting started.
Moscow has said it has the right to protect Russian speakers in Ukraine. It accuses the new Ukrainian leadership of being anti-Russian and anti-Semitic and of threatening the rights of pro-Russians.
But senior U.N. human rights official Ivan Simonvic told the Security Council Wednesday that during two trips to Ukraine in March, his team found no widespread attacks against ethnic-Russians.
Moscow calls the U.N. report biased and unfounded.
The tentative agreement could put on hold economic sanctions the West had prepared to impose on Russia if the talks were fruitless
And that would ease international pressure both on Moscow and nervous European Union nations that depend on Russia for their energy.
Kerry said "there was no discussion" of the removal of immediate sanctions.
Ukrainian and Israeli media are reporting that Jews in the eastern city of Donetsk -- where pro-Russian militants have taken control of government buildings -- were ordered to "register" with those who are trying to force the city to become part of Russia.
U.S. Ambassador to Ukraine Geoff Pyatt is confirming that "chilling" anti-semitic leaflets in Donetsk appear to be "the real deal."
Kerry also mentioned the reported anti-Jewish incident in eastern Ukraine, and a threat to the Russian Orthodox Church.
Kerry condemned the move. "In the year 2014, after all of the miles traveled and all of the journey of history, this is not just intolerable, it's grotesque. It is beyond unacceptable," he told reporters.
Lisa Schlein in Geneva and Luis Ramirez at the White House contributed material for this report