The Ukrainian military says one of its helicopters has been shot down by pro-Russian rebels in the east, killing all nine people on board.

It says the Mi-8 helicopter was hit by a rocket shortly after take-off outside the rebel-held city of Sloviansk.

It comes a day after the rebels vowed to observe a ceasefire until Friday, in response to a government peace plan.

But Ukraine's president said he may end it due to "constant violation by rebels who are controlled from abroad".

A statement from Petro Poroshenko's office said "the head of state does not exclude that the ceasefire regime may be revoked ahead of schedule".

Earlier, Russia's president warned that the week-long truce was not enough.

Vladimir Putin said it should be extended to try to hold "substantive talks" between the Ukrainian government and the separatists.

The rebels have not commented publicly on the Ukrainian military's claims.

Before Tuesday, the rebels - who continue to hold towns in the regions of Donetsk and Luhansk - had shot down at least two Ukrainian army helicopters and a plane.

BBC