Standoff: A checkpoint manned by an assortment of Ukrainian military personnel outside the town of Slavyansk in eastern Ukraine. Photo: Kate Geraghty
The US and France have warned Russia of new sanctions if Moscow keeps up its "provocative and destabilising behaviour" in Ukraine, just over a week before the former Soviet republic is due to hold a presidential election.
The warning came as the United Nations sounded the alarm on deteriorating human rights in eastern Ukraine, citing abuses which it said were carried out by pro-Russian separatists.
In a veiled reference to Russia, UN High Commissioner for Human Rights Navi Pillay called on those with influence on the armed groups in the east "to do their utmost to rein in these men who seem bent on tearing the country apart".
In a phone call, US President Barack Obama and his French counterpart Francois Hollande "underscored that Russia will face significant additional costs if it continues its provocative and destabilising behaviour", the White House said in a statement.
Mr Obama has drafted an executive order for sanctions across key sectors in Russia such as banking, energy, defence and mining.
With the May 25 election fast approaching, Kiev's interim leaders are struggling to keep the country from disintegrating further after Moscow's disputed annexation of Crimea in March.
Government forces are finding it an uphill battle to crush the bloody rebellion in Ukraine's industrial belt where insurgents have seized more than a dozen towns and cities in just a few weeks.
In a new report, the UN rights chief catalogued a series of "targeted killings, torture and beatings, abductions, intimidation and some cases of sexual harassment", which she blamed on the anti-government groups in the east.
The West has been pushing an OSCE (Organisation for Security and Cooperation in Europe) peace plan to try to resolve the escalating crisis on Europe's doorstep, while threatening further sanctions if Moscow or its "proxies" disrupt the election.
Two of the main eastern regions, Donetsk and Lugansk, have already proclaimed sovereignty after weekend independence referendums rejected as illegal by Kiev and the West, raising concerns about how elections will be conducted in rebel-held areas.
Dr Pillay also voiced deep concern about harassment and intimidation of ethnic Tatars in the Crimean peninsula, which was annexed by Russia in the face of international outrage.
US Secretary of State John Kerry also denounced fresh rights abuses of Crimea's Tatars, saying in a statement: "Russia's occupation and illegal attempt to annex Crimea has reopened old wounds.
"The list of human rights abuses committed today in Crimea is long and grows longer with each passing week.
"Murder, beatings and the kidnapping of Crimean Tatars and others have become standard fare."
But Moscow blasted the UN report as biased in favour of Kiev's leaders, who took power in February after months of pro-EU protests that led to the ousting of Kremlin-backed president Viktor Yanukovych.
"The complete lack of objectivity, blatant discrepancies and double standards leave no doubts that (the report's) authors were performing a political put-up job aimed at clearing the name of the self-declared authorities in Kiev," the foreign ministry said.
Mr Kerry on Thursday urged Moscow against disrupting the election -- seen as key to preventing the country from descending into all-out war.
"Our message is really, quite simple: 'Let Ukraine vote. Let the Ukrainian people choose their future'," he said, accusing the rebels of "seeking to speak for everybody through the barrel of the gun".
While Moscow has scaled back its vehement opposition to the vote, Foreign Minister Sergei Lavrov has questioned how it could take place against a backdrop of bloodshed.
"When Ukrainians kill Ukrainians I believe this is as close to a civil war as you can get."