Ukraine street battles in Luhansk as troops advance
Heavy fighting has been reported in rebel-held areas of eastern Ukraine, with street clashes in the centre of the key city of Luhansk.
Government forces have regained one district in the city, officials say.
Shelling has been reported near the rebel headquarters in Donetsk, the other major rebel-held eastern city.
Russia says President Vladimir Putin is due to meet Ukraine's Petro Poroshenko next week, as the number of civilian casualties rises.
Pro-Russian separatists in the eastern regions of Luhansk and Donetsk declared independence from Kiev and proclaimed their own people's republics after Russia annexed the Crimean peninsula from Ukraine in March.
More than 2,000 civilians and combatants have been killed since mid-April, when Ukraine's government sent troops to put down the rebel uprising.
Ukrainian military officials say at least 17 civilians were killed when a convoy of refugees came under mortar and rocket fire south-east of Luhansk on Monday.
Ukraine accuses Russia of arming the rebels and sending Russian soldiers into eastern Ukraine - a claim denied by the Kremlin.
'Block by block'
The city centre of Luhansk was reported to have been shelled on Monday night and video filmed hours earlier appeared to show deserted streets.
Tens of thousands of civilians have fled in recent weeks as Ukrainian government forces have advanced on Luhansk. The city is suffering acute shortages of water, food and electricity.
An interior ministry aide told the Interfax Ukraine agency that the military was recapturing the city "block by block".
At the same time, reports said a convoy of armoured vehicles from Russia had managed to enter Luhansk to help the rebels.
The claim was made by prominent Ukrainian military journalist Dmytro Tymchuk, who said there had been "dozens of pieces of of military hardware".
Russia has repeatedly denied sending any weapons across the border.
The separatists have lost control of several small towns in both regions in recent days.
TV channels banned
Residents in the centre of Donetsk fled as the rebel headquarters came under shell fire. Cars with gunmen sped through red lights, Reuters news agency reported.
Clashes were also reported in Makiivka, east of the city, hours after government forces said they had taken control of most of the town of Ilovaisk, to the south-east.
A prominent pro-Ukraine commander, Semen Semenchenko, suffered shrapnel wounds when his unit came under mortar attack in Ilovaisk. He is considered one of the most popular of the volunteer commanders in the country.
An aide to Ukraine's interior ministry, Anton Gerashenko, said that 14 Russian TV channels had been banned from cable networks in Ukraine.
The channels, including Russia Today and Life News, had been "broadcasting propaganda of war and violence", Mr Gerashenko said.
Meanwhile, the death toll from an attack on a convoy of refugees in the Luhansk area on Monday has risen to 17, Ukrainian military spokesman Andriy Lysenko says.
Details of what happened are unclear. Ukraine has accused pro-Russian rebels of attacking the convoy with Grad rockets and mortar rounds on a road between Novosvitlivka and Khryashchuvatye.
A rebel source, however, told the BBC that everyone in the convoy was killed when two buses carrying wounded civilians came under fire from foreign mercenaries fighting for the government.
'Torn to bits'
The defence ministry in Kiev has posted a video which it says shows survivors describing what happened.
One man describes a car being "torn to bits" by a mortar round while another says his mother-in-law died instantly and his daughter bled to death.
Later in the defence ministry video, a soldier says two Zil lorries carrying refugees were hit by two mortar rounds. One was damaged and the other completely destroyed, he says.
The BBC has been unable to independently verify the video.
Establishing who attacked the convoy will be difficult as both sides have supplies of the Russian-made Grad rockets.
Diplomatic efforts to seek a solution to the crisis intensified on Tuesday.
German Chancellor Angela Merkel is to meet Ukrainian officials on Saturday, on her first visit to Kiev since the crisis began.
Talks are then due to take place on 26 August between the Russian and Ukrainian presidents in Belarus. EU foreign policy chief Catherine Ashton will also attend the meeting.
In a separate move, the Council of Europe, to which Ukraine and Russia both belong, urged member states on Tuesday to "step up humanitarian aid" in eastern Ukraine, saying that the number of displaced people and refugees was "increasing rapidly".
Eastern Ukraine - the increasing human cost
- At least 2,119 have died since mid-April, including at least 20 children
- 5,043 people have been wounded in east Ukraine as of 13 August
- On average 60 casualties per day
- 155,800 people internally displaced
- 188,000 have fled to Russia
- 22,000 people have fled Donetsk and Luhansk in a five-day period last week