Ukraine crises: Obama unveils fresh sanctions on Russia

US President said sanctions would include export restrictions on high-tech goods in a bid to ratchet up pressure

President Barack Obama said today the United States was poised to unveil fresh sanctions against Russia over the crisis in Ukraine, as pro-Kremlin gunmen seized another town in the east.

Speaking in the Philippines, Obama said the sanctions would include export restrictions on high-tech goods in a bid to ratchet up pressure on Russian President Vladimir Putin, blamed for the worst East-West crisis since the Cold War.

Separately, top EU officials were to meet in Brussels to step up European sanctions on Russia as part of a coordinated global effort against Moscow.

On the ground in eastern Ukraine, tensions remained at fever pitch as gunmen stormed the town hall and police offices in Kostyantynivka, the latest in a string of assaults by insurgents on towns in the region.

Rebels also refused to release a group of international monitors from the OSCE after presenting them to the media as "prisoners of war" in what Germany said was a "repugnant" display.

Meanwhile, the threat of a full-scale invasion loomed large over the ex-Soviet country, with tens of thousands of Russian troops massed on the border and Ukraine's prime minister warning of efforts to start a "third world war".

On the last leg of a four-country Asia tour, Obama announced new steps to punish Russia for what the president has called "provocation" on Ukraine's border, where Moscow has conducted military operations.

"Later today, there will be an announcement made. It builds on the sanctions that were already in place," Obama told reporters.

He said Washington would unveil a list of "individuals and companies" that will be sanctioned to build pressure on Putin and Russia's recession-hit economy.

He added the measures would also focus on "high-tech defence exports to Russia" that he said were not appropriate given the tensions between Moscow and the West.

The sanctions are in response to Russia's perceived lack of action to implement an April 17 accord struck in Geneva to defuse the crisis. Obama has said Moscow has not "lifted a finger" to enact the deal.