By James Mates: Europe Editor from Mariupol, east Ukraine

It has been a quiet evening here in Mariupol - almost unnaturally quiet so used are we to the booms of artillery.

There are no reports of any breaches of today's announced ceasefire elsewhere in east Ukraine, but nonetheless it is hard not to share Barack Obama's scepticism.

The two sides are miles apart - the rebels insisting that they are going to separate from Ukraine, and the Ukrainians insisting they will hold on to their territorial integrity.

The real question here is who blinked to bring this ceasefire into being.

Ukraine President Petro Poroshenko announced the ceasefire from the Nato summit in Wales today. Credit: Reuters

Was it, as President Obama suggested in his press conference, Russia buckling under the weight of sanctions and sanctions still to come?

Or was it - and I think this is much more likely - a case of the Ukrainians trying to cut their losses?

For ten days, rather than fighting a rag-tag rebel army, they have been facing highly professional Russian troops and armour and coming off very distinctly second best.

Pro-Russian rebels retain authority in large parts of eastern Ukraine. Credit: Reuters

Now they face the prospect of losing significantly more territory which they may never get back.

We may not know the answer to who is on top until one side or the other starts making compromises.

But the ceasefire may not even last long enough for substantive talks to begin.