600 Russian troops started military exercises in Crimea, state media reported on Tuesday. Using 50 units of heavy weaponry, Russia's Black Sea Fleet is conducting their maneuvers a day before a four-way summit in Minsk for resolving the crisis in Ukraine, which began when Russia annexed Crimea last March.

At the same time, a further 2,000 soldiers started large-scale exercises in southern Russia near the border with Ukraine in a show of military might ahead of the crisis talks.

Ukrainian President Petro Poroshenko, his Russian counterpart Vladimir Putin, along with European duo Angela Merkel and Francois Hollande are heading to the Belarusian capital in the hopes of reviving an earlier ceasefire that crumbled almost as soon as it was agreed upon.

Both sides claim advances

As world leaders press for a diplomatic solution to the fighting between pro-Russian separatists and Ukrainian government forces in the east of the country, both sides claim to have made significant gains on the ground on Tuesday.

Ukrainian troops launched an offensive against the rebels in the port city of Mariupol, breaking through their defenses, according to Ukraine's National Security Council. Meanwhile, conflicting reports came out of the town of Debaltseve- with both the Ukrainian Defense Ministry and the separatists claiming on Tuesday that they were in control of the strategic rail hub and highway connection between the embattled cities of Donetsk and Luhansk.

Tuesday's fighting cost the lives of at least nine people, including two civilians. A further six civilians were killed when, according to regional police, rebel rocket fire hit the Ukrainian army's eastern headquarters in Kramatorsk, though the rebels denied the accusation.

es/rg (AP, dpa, Reuters)