THE US, Russia, Ukraine and the European Union have said all sides have agreed to action to "de-escalate" the crisis in Ukraine.

The agreement, reached after seven hours of negotiation, requires a halt to violence, intimidation or provocative actions.

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It calls for the disarming of all illegally armed groups and for control of buildings seized by ­pro-Russian separatists during the protests to be turned back over to authorities.

It also gives amnesty to protesters who comply with the demands, except those found guilty of committing capital crimes.

President Barack Obama said the crisis talks in Geneva between Russia and western powers were promising but that the US and its allies were prepared to impose more sanctions on Russia if the situation fails to improve.

Russian President Vladimir Putin, speaking in Moscow, accused Ukraine's leaders of committing a "grave crime" by using the army to try to quell unrest in the east of the country, and did not rule out sending in Russian troops. Mr Putin said he hoped he would not need to take such a step, and that diplomacy could succeed in resolving the standoff, the worst crisis in East-West relations since the Cold War.

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The comments came hours after separatists attacked a Ukrainian national guard base and Kiev said three of them were killed in the worst bloodshed yet in a 10-day pro-Russian uprising.

Ukrainian, Russian and Western diplomats were seeking to resolve a confrontation that has seen pro-Russian fighters seize official buildings across Ukraine while Moscow masses tens of thousands of troops on the frontier.

"All sides must refrain from any violence, intimidation or provocative actions," a joint statement said. "All illegal armed groups must be disarmed; all illegally seized buildings must be returned to legitimate owners; all illegally occupied streets, squares and other public places in Ukrainian cities and towns must be vacated."

Mr Obama said: "There is the possibility, the prospect, that diplomacy may de-escalate the situation. The question now becomes, will in fact they use the influence they've exerted in a disruptive way to restore some order so that Ukrainians can carry out an election and move forward with the decentralisation reforms that they've proposed?"

It was unclear if Russia would meet Western demands for it to stop stirring unrest in the east and withdraw its troops from the Ukrainian border. Moscow denies it is active in Ukraine.

"It will be a test for Russia, if Russia wants really to show willing to have stability in these regions," said Ukrainian Foreign Minister Andriy Deshchytsia.

The US State Department said the talks had achieved more than some people had expected. But a spokeswoman added: "But again, it's not a breakthrough until this is implemented on the ground, and we need to see the Russians follow up these words with actions."

There is scepticism over whether the agreement will work.

"Diplomacy cannot succeed if there is no room for compromise," said Ulrich Speck, a visiting scholar at Carnegie Europe. "The Kremlin is dedicated to get Ukraine under its control, one way or another."

US Secretary of State John Kerry said there would be additional sanctions against Russia if it did not act to calm tensions in Ukraine. "If ... we don't see a movement in the right direction, then there will be additional sanctions, additional costs as a consequence," he said.