How long can Western unity over Ukraine hold?

"You only have to look at the struggle to get the oil embargo," says Ian Bond, director of foreign policy at the Centre for European Reform, referring to the tortured weeks of negotiation that resulted in this week's partial EU embargo on Russian oil.

..."There's a kind of calibration going on," says Ian Bond. "As though we're saying 'we want the Ukrainians to win but not to win too much'".

..."If either side begins to make decisive gains, then they become more of a problem," says Ian Bond.

"If the Russians completely break through Ukrainian lines in the east and start heading for the Dnieper River, the question of how much territory Ukraine should be willing to sacrifice to achieve a ceasefire is going to move up the agenda."

By the same token, if Ukrainian forces start driving the Russians back, Ian Bond says, "there will be voices in the West saying 'don't try and recapture parts of the Donbas that the Russians have controlled since 2014'."