Both Ukrainian and Russian sources reported that Ukraine had captured the villages of Verbivka and Volokhiv Yar and had “operationally surrounded” the town of Balakliya. The advances which haven’t been officially confirmed by Moscow or Kyiv would place Ukrainian soldiers at least a dozen miles behind the Russian front line.
It would also mean that they could potentially threaten key supply lines to Russian forces in northern Donbas.
The Ukrainian army and government did not formally announce that the assault near Balakliya had begun on Tuesday.
However, an anonymous official told The Daily Telegraph that the offensive had been planned for a long time.
It was designed to catch the Russians off guard while their generals were focusing on counteracting the Ukrainian offensive in the southern Kherson region, the source added.
They said: “The Russians sort of expected it down there, and part of it is to attack them seemingly independently but in different locations so they never know where.
“The first objective is to throw the Russians out of Kharkiv region and the second objective is to create a platform to start approaching Izyum.
“So far it has been pretty successful.”
Pro-Ukrainian bloggers posted videos online on Wednesday morning which claimed that Ukrainian troops were in the village of Verbivka outside Balakliya and in the centre of Volokiv Yar.
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Alexander Kots war correspondent for Russian tabloid Komsomolskaya Pravda wrote on Telegram that it was likely that Ukraine was looking to cut off the Russian command centre in this part of the front.
He said: “They do not have the objective of taking Balakiye at all costs.
“If the enemy moves through Shevchenko to Kupiansk, the Izyum grouping will in fact be cut off from the [Russian] mainland.”
He added that Russian forces should consider withdrawing eastwards in order to avoid being encircled.
Izyum is a key junction on the border of the Kharkiv and Donbas regions and its loss would represent a major blow to Moscow.