Ukraine's Western allies on Wednesday promised to make Russia pay for its invasion, as governments and private investors met to fund the country's reconstruction from the ravages of war.

The World Bank has put an estimate of $14 billion on Ukraine's immediate needs to repair the damage caused by the bitter fighting.

But a recent study by the World Bank, the UN, the European Union and the Ukrainian government said the wider recovery of the economy would cost $411 billion.

Delegates, from Ukraine's Prime Minister Denys Shmygal to UK Prime Minister Rishi Sunak and US Secretary of State Antony Blinken, said the Kremlin would ultimately foot the bill.

"Let's be clear: Russia is causing Ukraine's destruction," Blinken told delegates at a London conference.

"And Russia will eventually bear the cost of Ukraine's reconstruction."

Sunak promised to keep tough sanctions in place "until Russia pays up", and to use seized assets to get Ukraine back on its feet -- something the European Union said it would also look at.

In an indication of the sheer scale of the reconstruction needed, Shmygal said the destruction of the Russian-held Kakhovka dam earlier this month caused an estimated $1.5 billion in environmental damage.

But that did not include losses in agriculture, infrastructure and housing, let alone how much it would cost to rebuild the plant.

- Support - 

Ukraine's President Volodymyr Zelensky is overseeing a military fight-back using Western-supplied heavy weaponry to regain territory lost to Russian forces since last year.

"Every day of Russian aggression brings new ruins, thousands and thousands of destroyed houses, devastated industries, burnt lives," Zelensky told the conference by video link.

In Kramatorsk, eastern Ukraine, on Wednesday, AFP saw locals rebuilding homes after a deadly Russian missile attack.

"Everything is destroyed," said local volunteer Bogdan. "If we're talking about restoring houses so you can shelter from the rain and live, I think the work here will take a week.

"If we're talking about a full recovery, then a year, two, three... I don't know."

Zelensky set out his stall for future investment, saying that despite the devastation, Ukraine was ripe for development in sectors from technology and green agriculture to clean energy.

Leaders and representatives from more than 60 countries are attending the International Ukraine Recovery Conference 2023 -- the second to be held since the Russian invasion in February last year.

The first, in Lugano, Switzerland, last July saw allies commit to supporting Ukraine through what is expected to be an eye-wateringly expensive and decades-long recovery.

UK Foreign Secretary James Cleverly told reporters he was "completely confident" the world would find the funds.

But African countries have voiced concern that by pumping aid to Ukraine, the West is backing off from pledges to help the continent with development and fight climate change.

Sunak told delegates that Kyiv's allies would support Ukraine "on the battlefield and beyond" for as long as it takes.

Zelensky underscored the need for long-term support. 

"Some people believe this is a Hollywood movie and expect results now," he told the BBC in a separate interview.

"It's not. What's at stake is people's lives," he added, calling Russia's Vladimir Putin "the second king of antisemitism after Hitler".

Putin last week said Zelensky, who lost relatives in the Holocaust, was "a disgrace" to the Jewish people.

- Private sector - 

Sunak has announced UK backing for Ukraine to the tune of $3 billion so it can unlock vital World Bank loans to help bolster public services, including schools and hospitals.

The guarantee will run over the next three years, he said. He also announced an extra £240 million ($306 million) in development aid funding for humanitarian projects.

European Commission president Ursula von der Leyen recapped the EU executive's support package for Ukraine of 50 billion euros ($55 billion) over the next four years. 

Germany will provide 381 million euros in humanitarian assistance this year and France 40 million euros.

The United States will provide more than $1.3 billion in additional aid.

As well as government support, it is hoped more private-sector firms will join the reconstruction effort.

Delegates include captains of industry from major multinationals and corporations, many of whom have signed up to a new Ukraine Business Compact.

It encourages trade, investment and expertise-sharing to Ukraine on the back of promises from Zelensky to tackle barriers such as corruption and financial and legal transparency.

More than 400 companies from 38 countries, with a combined market capitalisation of $4.9 trillion, have already promised to back Ukraine's recovery and reconstruction, Sunak said.

burs-phz/jwp/jj