Ukrainian troops have attacked pro-Russian separatists in the southern port of Mariupol, officials said.

Four soldiers were wounded as government forces retook buildings occupied by rebels in the centre of town, according to interior minister Arsen Avakov.

He said troops also destroyed a light armoured vehicle used by the separatists.

The renewed fighting comes as rebel leaders confirmed they have three tanks. Ukrainian officials say the tanks crossed from the Russian side of the porous border and were attacked by Ukrainian troops, but there has been no independent confirmation the tanks come from Russia.

Rebel leader Denis Pushilin told Russian state television the separatists, who call themselves the Donetsk People's Republic, have the tanks. He said it was "improper to ask" where they came from.

Ukraine and the West have accused Moscow of fomenting the unrest in the east, but Russia has denied sending troops or weapons to Ukraine.

Ukrainian president Petro Poroshenko, who took office less than a week ago, yesterday rallied support for his plan to end fighting, in phone calls with Russian president Vladimir Putin and German chancellor Angela Merkel.

Mr Poroshenko told Ms Merkel he was willing to negotiate, but not with what he called terrorists, and could offer amnesty to those who did not have "blood on their hands".

According to his spokesman, Svyatoslav Tsegolko, he told Mr Putin it was "unacceptable" that tanks had crossed the border, while a Kremlin statement said Mr Poroshenko told Mr Putin about his plan for resolving the crisis.