The US and its leading European allies are preparing wider sanctions on Russia's economy and are discussing a ban on the export of high-tech energy equipment if Moscow is seen to disrupt Ukraine's presidential elections on May 25.
The west is backing the presidential poll to re-legitimise Kiev's leadership, even as separatist leaders in Donetsk, eastern Ukraine, asked Russia to annex it, following what they claimed was a resounding victory in a self-rule referendum on Sunday.
On Tuesday, Germany's foreign minister Frank-Walter Steinmeier travelled to Ukraine on a bridge-building mission that will also take in the southern and eastern regions.
Mark Dubowitz of the Foundation for Defense of Democracies, a think-tank, said such a move would follow the example of similar restrictions imposed on Iran.
"It would have a deleterious effect on Russia's production in the long term, without causing short-term disruption in energy markets," he said.