Ukraine on Thursday accused Russia of continuing the latest military build-up along the border of the two countries.
Spokesman Andriy Lysenko, quoting the Security Council in Kiev that some 60 armoured vehicles, including 50 T-64 tanks, were moved by train to a town close to the border in Russia’s southern Rostov region.
“The vehicles were not marked with national symbols’’, Lysenko said.
NATO Secretary General, Jens Stoltenberg, said earlier this week that Russian troops were again moving closer to the Ukraine border.
Ukraine and the West accuse Russia of covertly supporting the pro-Russian separatists in eastern Ukraine by training and equipping them and by sending volunteers and Special Forces across the border.
However, Russia denies those accusations.
The situation in the conflict zone remained tense on Thursday.
Authorities in Donetsk said that artillery fire could be widely heard throughout the city.
Fighting in Donetsk, which has a peacetime population of over one million, has continued despite a ceasefire agreed in September.
It is centred on the airport, which is being stubbornly defended by Ukrainian government troops.
On Wednesday, two children were killed when a grenade hit a school pitch close to the airport where they were playing football.
The security situation deteriorated after the separatists held leadership elections on Sunday, which were rejected by Ukraine, the European Union and the United States.
No fewer than 3,600 people have been killed since the violent conflict between pro-Russian separatists and Ukrainian government forces began in April.
Meanwhile, a group of Dutch experts continued to search the crash site of Malaysia Airlines flight MH17 east of Donetsk.
The six experts were accompanied by members of the observer mission of the Organization for Security and Co-operation in Europe (OSCE), Russian news agencies reported.
All 298 people on board, 196 of them Dutch, were killed when the Boeing 777, which was flying from Amsterdam to Kuala Lumpur, crashed on July 17.
So far, the remains of 289 victims have been identified.
An official Dutch investigation found that the plane was probably hit by a surface-to-air missile but named no culprit.
However, Ukraine and separatist rebels have blamed each other for the incident.