Britain has joined international condemnation of rebels in two eastern Ukrainian regions as they stage sovereignty referendums.
Separatists are going ahead with votes in Donetsk and neighbouring Luhansk despite Russian president Vladimir Putin's surprise call on Wednesday to delay the vote.
Ukrainian president Oleksandr Turchynov warned that the poll is a "step into the abyss for the regions" and insisted the rebels "don't understand that this would be a complete destruction of the economy, social programs and general life for the majority of the population".
Mariupol, in the Donetsk region, was the scene of fierce clashes between Ukrainian government forces and pro-Russia protesters on Friday that left seven people dead.
German chancellor Angela Merkel and French president Francois Hollande appealed for Mr Putin to send more "signals of de-escalation" ahead of the "illegitimate" vote. It is unclear whether the results will be endorsed by Moscow.
Voters will be asked if they approve the creation of sovereign and independent "people's republics" but organisers want to then hold a second poll on whether to seek to become part of Russia.
Britain urged the rebels to listen the Russian premier's calls for a delay and stressed it would not recognise the result of the poll.
A Foreign Office spokeswoman said: " We hope that separatists in the east of Ukraine will have heard the words of President Putin on May 7 about the May presidential election being a step forward and about not going ahead with the so-called referendum in Donetsk this weekend.
"The Ukrainian constitution does not permit this referendum. We do not and will not recognise its legitimacy."