The Russian-backed leader of the breakaway Donetsk region said on Wednesday he wanted to peacefully settle its borders with Ukraine but reserved the right to ask “big Russia” for help.

Denis Pushilin, who heads the self-proclaimed Donetsk People’s Republic that was recognised by Russia this week, said he favoured dialogue with Ukraine in the first instance.

But he told a news conference the situation in their long-running conflict had become critical and the separatists had accelerated a mobilisation of forces, in which healthy men between 18 and 55 have been called up to fight.

“We will win. With people like this, we will win. With such a country, with big Russia, which we respect and value,” he said. “We have no right to lose, or even to doubt in our victory.”

Russia’s recognition of Donetsk and the neighbouring self-proclaimed Lugansk People’s Republic on Monday was declared illegal by Western countries, which have imposed new sanctions against Moscow.

The move has taken the Ukraine crisis into a new phase as the treaties Russian President Vladimir Putin signed with separatist leaders on Monday provide a legal pretext for Russia to send in its forces in support of the separatists, who now control only a fraction of the two regions of eastern Ukraine that they claim.

Asked if they would try to expand their territory, Pushilin said: “We are not yet at that stage, we’re at the stage when the enemy’s forces are on the line of contact and can move onto the offensive at any moment.”

Ukraine strongly denies accusations by the separatists that it is bent on recapturing territory by force, and has rejected a series of Russian and separatist reports about alleged attacks.

Speaking alongside Pushilin, Andrey Turchak, a senior member of Russia’s ruling party, said no force in the world could change the legal result of Russia’s recognition.

“For us, the slogan ‘Russia doesn’t abandon its own people’ – these are not empty words,” Turchak said. “I am glad we have all united around this idea, the Russian idea, the restoration and preservation of the Russian world.”

He said it was unlikely that any agreement could be reached with the current Ukrainian government.