Ukrainian forces have raised their national flag over a police station in the city of Luhansk which was for months under rebel control, Kiev said yesterday, in what could be a breakthrough in Ukraine’s efforts to crush pro-Moscow separatists.

Ukrainian officials allege though that the rebels are fighting a desperate rearguard action to hold on to Luhansk which is their supply route into neighbouring Russia and say the flow of weapons and fighters from Russia has accelerated.

The foreign ministers of Ukraine and Russia were preparing to meet for talks on the conflict in Berlin yesterday, though it seemed likely that the diplomacy could be overshadowed by fast-moving developments on the battlefield.

Separatists shot down a Ukrainian warplane

Russia denies helping the rebels and accuses Kiev, backed by the West, of triggering a humanitarian crisis through indiscriminate use of force against Russian speakers in eastern Ukraine who reject the Ukrainian government’s rule.

Andriy Lysenko, a Ukrainian military spokesman, said government forces fought separatists in a neighbourhood of Luhansk city on Saturday and took control of the Zhovtneviy neighbourhood police station.

“They raised the state flag over it,” Lysenko told a news briefing.

Separatist officials in Luhansk could not be reached by telephone, and a separatist spokeswoman in Donetsk, the other rebel strong-hold in eastern Ukraine, said she did not know what had happened in Luhansk.

A photograph posted on Twitter appeared to show a Ukrainian flag on the front of the police station, but it could not be independently verified.

If confirmed, the taking of the police station is significant because the city of Luhansk has for several months been a rebel redoubt where Kiev’s writ has not run.

Ukrainian servicemen guard a checkpoint near the eastern Ukrainian town of Debaltseve. Photos: Reuters

Ukrainian troops have been closing in on the city from the outskirts, but had not previously been able to get forces inside the city limits. The separatists still control sections of the border linking Luhansk region to Russia.

The four-month-old conflict in Ukraine’s Russian-speaking east has reached a critical phase, with Kiev and Western governments watching nervously to see if Russia will intervene in support of the increasingly besieged rebels.

The rebels have responded to the reverses with defiant rhetoric, and the fighting continues.

Ukrainian authorities said that the separatists shot down a Ukrainian warplane. The pilot ejected and was located and recovered after a search, a military spokesman told Reuters.

On Saturday, Alexander Zakharchenko, prime minister of the self-proclaimed Donetsk People's Republic, said rebels were in the process of receiving some 150 armoured vehicles, including 30 tanks, and 1,200 fighters trained in Russia.

He said they planned to launch a major counter-offensive.

“They are joining at the most crucial moment,” he said in a video recorded on Friday.