Ukraine’s military has accused Russia of sending more tanks and troops into the east of the country to support pro-Russian separatists.
NATO says it has seen an increase in Russian troops and equipment along the border between the two countries and is looking into reports that tanks crossed into Ukraine.
The Ukrainian authorities also claim government forces killed up to 200 rebels at Donetsk airport on Thursday.
None of the information has been confirmed.
Kyiv says the Russian incursion happened on Thursday.
“(The convoy) headed towards the town of Krasny Luch in the Luhansk region. The movement of military equipment was reported, consisting of 32 tanks, 16 D30 howitzer artillery systems, and 30 KAMAZ trucks carrying ammunition and fighters,” Andriy Lysenko, spokesman for the Ukrainian Defence and Security Council, told a news briefing.
Russia did not respond immediately to Kyiv’s latest accusations but said it still supported a ceasefire deal.
Yet the funerals on Friday for two teenagers killed in Donetsk’s western suburbs only strengthen a feeling that the Minsk accord is increasingly in tatters.
The school football pitch where a mortar shell killed 18-year-old Andrey Eliseev and 14-year-old Daniil Kuznetsov is not far from rebel positions which have often come under fire from government forces.
Amid the grief among families, school staff and classmates as the boys were laid to rest, one of their teachers accused the Ukrainian government of killing its own people.
“Ukraine isn’t killing dogs, it’s killing people! Why is everybody silent, why does nobody see us? Why do our children have to die? Why are we left to pray?” she cried.
Kyiv has denied responsibility for the attack, saying it was planned provocation by pro-Russian separatists.