President Vladimir Putin said on Friday that Russia's call-up of reserve forces to fight in Ukraine, criticized as chaotic by some Kremlin allies, had been vital to hold the front line but would be wound up in the next couple of weeks, News.az reports citing Reuters.

Russia has conducted a broad mobilization of Russians to reinforce its long front after Ukraine won back territory in recent weeks. Moscow has also threatened to use nuclear weapons to defend territory including four regions of Ukraine it annexed late last month but does not fully control.

"The line of contact is 1,100 km (680 miles), so it is practically impossible to hold it with forces formed only of contract soldiers, especially since they take part in offensive activities," Putin told a news conference at the end of a summit in Kazakhstan, adding that those mobilized were being properly trained.

Putin said there were no plans for new massive strikes on Ukraine "for now" after what Ukraine said was the firing of 100 Russian cruise missiles this week, mainly at its electricity and heat infrastructure.