New sanctions threat to Russia
Western leaders have warned Russia that it faces a fresh round of sanctions after failing to implement a deal to defuse the Ukraine crisis.
The need for further action was agreed in a conference call between Prime Minister David Cameron, US president Barack Obama, German chancellor Angela Merkel, French president Francois Hollande and Italian prime minister Matteo Renzi.
A Downing Street spokesman said: " They condemned the absence of any efforts on the part of Russia to support the implementation of the Geneva agreement, and the further efforts to destabilise Ukraine and to undermine the 25 May elections.
"While they continued to hold open the door to a diplomatic resolution of this crisis, based on the Geneva agreement, the five leaders agreed that in the light of Russia's refusal to support the process, an extension of the current targeted sanctions would need to be implemented, in conjunction with other G7 leaders and with European partners."
According to a readout of the call issued by the White House, the leaders criticised Russia for "not publicly supporting the Geneva accord, nor calling on armed militant groups to lay down their arms and leave the government buildings they've occupied".
Moscow had "in fact continued to escalate the situation through its increasingly concerning rhetoric and threatening military exercises on Ukraine's border".
In increasingly bitter diplomatic exchanges, Russian foreign minister Sergey Lavrov has accused the West of plotting to control Ukraine.
He said pro-Moscow insurgents in the south east of the country would lay down their arms only if the Ukrainian government cleared the Maidan protest camp in the capital Kiev.
"The West wants - and this is how it all began - to seize control of Ukraine because of their own political ambitions, not in the interests of the Ukrainian people," Mr Lavrov said.
But US secretary of state John Kerry said: "For seven days, Russia has refused to take a single concrete step in the right direction.
"Not a single Russian official, not one, has publicly gone on television in Ukraine and called on the separatists to support the Geneva agreement, to support the stand-down, to give up their weapons, and get out of the Ukrainian buildings."
Ukrainian prime minister Arseniy Yatsenyuk has accused Russia of wanting to start "a third world war".
There are reports that a Ukrainian military helicopter in the eastern town of Kramatorsk has been shot down by Russian supporting insurgents.
The agreement struck between Russia and Ukraine in Geneva last week was hailed as a breakthrough, and called for all parties to down arms and vacate public buildings.
Pro-Russian militia have been occupying government buildings in more than 10 cities in the eastern Ukraine while the nationalist Right Sector movement is still in control of two public buildings in Kiev.