Nato has pledged to give more weapons to Ukraine and help fix critical energy infrastructure badly damaged by massive Russian missile and drone strikes.

At a gathering in Berlin, justice ministers of the G7 group of wealthy nations said they would co-ordinate investigations into alleged war crimes committed in Ukraine.

Russian President Vladimir Putin - who ordered a full-scale invasion of Ukraine on 24 February - and other senior Kremlin officials deny the allegations that Russian troops are committing war crimes.

Speaking at the start of the two-day gathering of Nato foreign ministers in the Romanian capital, Mr Stoltenberg said: "Russia is actually failing on the battlefield.

Later on Tuesday, Nato issued a statement that said Russia's persistent attacks on Ukrainian civilian and energy grids were "depriving millions of basic human services".

Nato members would assist Ukraine in repairing its energy infrastructure and protecting people from missile attacks, the statement added.

And appearing at a joint news conference with Ukrainian Foreign Minister Dmytro Kuleba, Mr Stoltenberg said: "We will stand by Ukraine as long as it takes, we will not back down.

Meanwhile, Mr Kuleba said that last time he met senior Nato officials his three words were "weapons, weapons, weapons".

Estonian Foreign Minister Urmas Rainsalu later told BBC World Service's Newshour programme that Nato needed to give missiles to Ukraine that can hit inside Russian territory.

The US-led Nato alliance has repeatedly ruled out supplying longer-range missiles and other such weaponry to Ukraine, amid concerns that this could lead to a major escalation with a nuclear-armed Russia.

In Ukraine, energy workers across the country are continuing their daunting task of repairing power and water supplies to millions of people, amid warnings that Russia maybe preparing a new wave of missile attacks.