It looks like a carbon copy of what President Putin did in March 2014, seizing the Crimea region from Ukraine, calling a referendum widely condemned by the international community and then annexing it anyway, through exactly the same constitutional process culminating in a vote in Russia's supportive parliament.

Except that it isn't. Crimea was seized with little bloodshed and came under total Russian control.

To varying degrees, all four of the regions now being annexed are still partially in Ukrainian hands. Together they make up 15% of Ukrainian sovereign territory.

The two eastern regions have been partly held by Russian-backed separatists since 2014, but after seven months of war only 60% of Donetsk can be claimed by Russia, and Luhansk is at the centre of a major Ukrainian offensive. Russian forces could be within hours of losing the strategically significant town of Lyman.

Zaporizhzhia's regional capital is very firmly Ukrainian-run, although in reach of Russian missiles, and Ukrainian forces are only a few miles from the city of Kherson.

How can you annex four regions you don't even control? Whatever the answer, Russia's leader has clearly been in a hurry to do so, announcing the self-styled referendums with barely any notice.

In his annexation speech, President Putin called on Ukraine to cease fire and return to talks, but he was clear there would be no return of occupied territory to Ukraine. Much of his speech was a diatribe against the West.

Kremlin spokesman Dmitry Peskov said on Friday that any strike on annexed territory would be regarded as an act of aggression.