Ukraine rebel-held Donetsk sees 'heavy fighting'
Heavy fighting has erupted in a suburb of the rebel stronghold of Donetsk, in eastern Ukraine, local officials say.
At least two civilians were killed as government forces battled to retake the city from pro-Russia separatists, Donetsk city council confirmed.
Reports say powerful blasts and shooting were heard in the city.
Ukrainian government forces have made steady gains in recent weeks, encircling Donetsk and another rebel stronghold, Luhansk.Power cuts
"As of 17:00 (14:00 GMT), there are active military hostilities going on in the Petrovksy district of Donetsk," Donetsk city council said on Tuesday, quoted by Ukraine's Unian news agency.
Electricity has been cut in some parts of the district after shells hit substations in the area, Unian added.
It said that gunfire - including heavy weapons - could also be heard in other parts of the city.
Eastern Ukraine has been unstable since rebels declared independence from the authorities in Kiev in April.
At least 1,500 people, both civilians and combatants, are believed to have been killed and thousands more injured since Ukraine's new government sent in troops to put down the insurrection in the regions of Donetsk and Luhansk.
The rebels have since been pushed back to their strongholds in the two cities of the same name, though other pockets of resistance remain.
Separately on Tuesday, Russia called for an emergency meeting of the UN Security Council over the humanitarian situation in Ukraine, Russia's Itar-Tass news agency reports.
It comes after the UN revealed that the number of people fleeing the war in eastern Ukraine to other parts of the country had jumped from 2,600 to 102,600 inside two months.
The figures for early June to early August coincide with a sharp increase in fighting between pro-Russian separatist rebels and security forces.'Provocation'
Russian President Vladimir Putin has also ordered his government to prepare retaliatory measures against the latest round of Western sanctions imposed, local news agencies report.
But he said the measures must be carefully designed to avoid affecting Russian consumers.
Russia, which annexed Ukraine's Crimea region in March, has been accused of arming the rebels and has been targeted by US and EU sanctions. Russia denies the accusations.
In a sign of increasing tensions, Ukrainian defence spokesman Andriy Lysenko on Tuesday condemned Russia's plans to carry out military exercises in southern Russia, calling it "a provocation".
He said Russia had massed some 45,000 troops along its shared border with Ukraine.
Mr Lysenko also said that Ukrainian troops had retreated from Yasynuvata, a railway hub in the Donetsk region formerly under separatist control.
Meanwhile, the whereabouts of more than 300 Ukrainian soldiers who sought shelter inside Russia after being cut off by the rebels remain unclear.
The soldiers and border guards, who entered Russian territory on Monday, have been housed in tents supplied by the Russian border service while negotiations continue about their fate.
Russia says that 438 Ukrainian service personnel sought shelter near the town of Gukovo, in Russia's Rostov region, while the Ukraine government says there are 311 of them.