An armoured column including 32 tanks and 30 trucks has crossed into eastern Ukraine from Russia, Kiev says.
The trucks were carrying ammunition and fighters, said a military spokesman, but the BBC cannot confirm his report.
A fragile ceasefire has been in place since 5 September, although hundreds of people have been killed since then.
More than 4,000 people have died since fighting erupted in April after pro-Russian separatists seized control in the regions of Donetsk and Luhansk.
Friday, November 7, 2014
Morning Jolt: Our Vacation from Paying Attention to Ukraine & Russia Just Ended
◼ So it turns out Putin thinks he has more flexibility after the election, too - BBC via Jim Geraghty/NRO