Fugitive U.S. intelligence leaker Edward Snowden is being manipulated by Russian authorities, the former director of the U.S. National Security Agency reportedly said Thursday, adding that he believed the leaks would cost lives. 

General Keith Alexander, who retired in March, told the Australian Financial Review that Russia would be looking to capitalise on the fact that Snowden's leaks had been so disruptive and damaging to the US.

Russian President Vladimir Putin told rebels in Ukraine to halt plans for independence votes and said his troops have pulled back from the border, but his apparent change of heart received short shrift from Kiev and Washington.

Putin on Wednesday also hailed a planned May 25 presidential election in Ukraine -- previously condemned by the Kremlin -- as a "move in the right direction".

Russia's President Vladimir Putin on Wednesday told pro-Russian rebels fighting in east Ukraine to halt plans for independence referendums and said his troops had pulled back from the border, in a potential breakthrough in the worst showdown between Moscow and the West since the Cold War.

The Russian leader also hailed a planned May 25 presidential election in Ukraine -- previously criticized by the Kremlin -- as a "move in the right direction".

Russia is deploying covert fighters and "enormous propaganda" to prevent Ukraine holding a presidential election later this month, British Foreign Secretary William Hague said on Wednesday during a visit to Kiev.

If Moscow succeeds, it would be "a terrible blow to democracy," said Hague, who accused Russia of engineering an independence referendum in Ukraine's east this weekend to undermine the May 25 presidential poll.

Ukrainian presidential candidate and self-made billionaire Petro Poroshenko defended the deployment of security forces against pro-Russian rebels, during a visit to Germany on Wednesday.

"For terrorists we should find the language they understand and that is force," he told reporters, after talks with a senior member of Chancellor Angela Merkel's conservatives.

Pro-Russian rebels on Wednesday fought troops to try to regain strategic positions in east Ukraine, while the West threw its weight behind a last-ditch diplomatic bid to calm the crisis ahead of a crucial presidential election.

The head of the OSCE was in Moscow to appeal to Russian President Vladimir Putin to help calm hostilities in the former Soviet republic.

Russia is gearing up for hugely patriotic celebrations of its victory over Nazi Germany in World War II on Friday, but festivities in neighboring Ukraine will be muted amid fears of provocations.

The May 9 commemorations come at an extremely sensitive time for the two Slavic nations that fought side by side against Nazi Germany but are now locked in an unprecedented confrontation that threatens to tip Ukraine into civil war.

U.S. senators were split Tuesday over when to impose new sanctions on Russia, with Republicans saying President Barack Obama should not wait until Ukraine's upcoming election before slapping Moscow with sector-wide penalties.

The White House has said it remains prepared to impose biting new sanctions on Russia, which has annexed the Crimean peninsula and furthered its aggression in unrest-plagued eastern Ukraine, should its forces disrupt Ukraine's May 25 poll.

German Chancellor Angela Merkel said Tuesday it would be a "pity" if the Russian president were to "use" the commemoration of World War II victory for visiting Crimea.

Merkel was responding to a reporter's question about media reports that Vladimir Putin could attend a May 9 military parade in his first visit to the peninsula since Russia annexed the territory in March.

German Chancellor Angela Merkel said Tuesday it would be a "pity" if the Russian president were to "use" the commemoration of World War II victory for visiting Crimea.

Merkel was responding to a reporter's question about media reports that Vladimir Putin could attend a May 9 military parade in his first visit to the peninsula since Russia annexed the territory in March.