US President Barack Obama warned on Sunday the West will take further measures against Moscow’s “provocation” in Ukraine, where pro-Russian militants are holding a team of international observers as “prisoners of war”.
Speaking in Asia, Obama called for global unity over the crisis as Europe and the US prepare fresh sanctions against Moscow expected to come into force as early as Monday.
AFP reporters in the flashpoint city of Slavyansk in eastern Ukraine said tensions were running high at checkpoints. Militants were reinforcing defences around occupied buildings and ordering journalists away.
The local rebel leader in the town, which is at the epicentre of the crisis, said his men continued to hold a team of OSCE observers.
“In our town, where a war situation is going on, any military personnel who don’t have our permission are considered prisoners of war,” Vyacheslav Ponomaryov told reporters.
He added that the group’s driver, who had been seized with them on Friday, had been released, bringing the number of detainees in the mission to 12: eight Europeans and four accompanying members of the Ukrainian army.
Pro-Russia militias this month occupied a string of towns and cities in eastern Ukraine, sparking a military response from the Ukrainian army, which is laying siege to Slavyansk.
With nerves jangling around the world, a Western diplomat has said a Russian invasion of Ukraine in coming days could not be ruled out, with some 40,000 troops poised on the border.
Ukrainian Prime Minister Arseniy Yatsenyuk cut short a trip to the Vatican on Saturday to rush home to deal with the crisis, with has plunged East-West relations to their lowest point since the Cold War.
He has accused Russian warplanes of multiple incursions into Ukrainian airspace in an attempt to provoke Kiev into starting “a third world war”.
Speaking in Malaysia, Obama said Russia had “not lifted a finger” to implement a deal struck in Geneva on April 17 aimed at easing the crisis.
“So long as Russia continues down a path of provocation rather than trying to resolve this issue peacefully and de-escalate it, there are going to be consequences and those consequences will continue to grow,” he said.
He urged Russia to call on the militants in eastern Ukraine to leave occupied buildings and “participate with international observers and monitors rather than stand by while they are being bullied and in some cases detained by these thugs”.
Russia’s envoy to the Organisation of Security and Cooperation in Europe has said that Moscow will take “all possible steps” to secure the release of the OSCE team.
The Vienna-based OSCE said that eight of its observers had been detained in Slavyansk since Friday - four Germans, a Pole, a Dane, a Swede and a Czech.
The chief of the insurgents’ self-styled “Republic of Donetsk”, Denis Pushilin, has accused them of being “Nato spies” and offered to release them only as a prisoner swap.
Ponomaryov said they were being held in the Town Hall, insisting they were “not our hostages - they are our guests” and stressing they were “doing well”.
He also confirmed that a team of negotiators from the OSCE - the Organisation for Security and Cooperation in Europe - would be arriving in Slavyansk later on Sunday to discuss the situation.
Ukraine’s own security services said they being were held as “human shields” in “inhuman conditions” and that one of the group required urgent medical attention that was being denied.
Ponomaryov added that the rebels were also holding three Ukrainian military officers captured overnight on what he said was a spying mission.
As the crisis worsens, the Group of Seven leading economies and the European Union are readying sanctions that could be announced as soon as Monday in a bid to raise the pressure on Russian President Vladimir Putin.
In a statement on Saturday, the G7 - comprising the United States, Britain, Canada, France, Germany Italy and Japan - said it would “move swiftly to impose additional sanctions on Russia”.
The EU said top officials would meet on Monday to weigh further sanctions. A diplomat in Brussels said a list adding 15 people to the 55 Russians and Ukrainians already blacklisted by the EU had been approved in principle.
The US and EU have already targeted Putin’s inner circle with visa and asset freezes and imposed sanctions on a key Russian bank.
Obama stressed the need for a unified response.
“It’s important that we are part of an international coalition sending that message and that Russia is isolated in its actions,” he told reporters in Kuala Lumpur.
It was vital to avoid “falling into the trap of interpreting this as the US is trying to pull Ukraine out of Russia’s orbit, circa 1950. Because that’s not what this is about,” he said.
“We’re going to be in a stronger position to deter Mr Putin when he sees that the world is unified and the United States and Europe are unified rather than this is just a US-Russian conflict,” Obama said.
The confrontation escalated after Russia refused to accept the legitimacy of Kiev’s new pro-EU government, which came to power in February after four months of street protests forced the ouster of the Kremlin-backed president, Viktor Yanukovych.
While Obama has ruled out sending US or NATO forces into Ukraine, Washington has begun deploying 600 US troops to bolster Nato’s defences in nearby eastern European states.