Facebook on Monday became the latest US tech giant to announce new investment in Britain with hundreds of extra jobs but hinted its success depended on skilled migration after Britain leaves the European Union.

The premier social network underlined London's status as a global technology hub at a British company bosses' summit where Prime Minister Theresa May sought to allay business concerns about Brexit.

"London is absolutely a global hub for technology," Nicola Mendelsohn, Facebook's vice president for Europe, the Middle East and Africa told the Confederation of British Industry (CBI) conference.

Mendelsohn said Facebook would open its new headquarters in the British capital next year, taking its UK workforce to 1,500 from around 1,000 now.

"It's a place where, frankly, our engineers want to come and work," she said, stressing that the company had staff from 65 nationalities working in London.

"The movement of talent is something that obviously matters to us," she said, although she added it was "too early to say" what effect Brexit could have.

Facebook's announcement comes one week after Google confirmed it would expand its vast London campus in a move that could bring 3,000 more jobs to the city.

Apple earlier this year also said it would create a new London headquarters in the iconic and long-abandoned Battersea Power Station in 2021.

May hailed the investments in her speech to the CBI saying she wanted Britain to be "the global go-to place for scientists, innovators and tech investors."

She also promised extra funds for research and development, as well as aiming for an "early agreement" on the status of EU nationals working in Britain after Brexit -- a key concern for businesses.

- 'Envy of Europe' -

London Mayor Sadiq Khan welcomed Facebook's announcement as "further evidence that London's strength as a tech hub keeps on growing".

"The capital's vibrant tech scene is the envy of Europe and Facebook's continuing commitment is another sign that London is open to talent, innovation and entrepreneurship from all four corners of the world."

Facebook last month unveiled an intra-office network called "Workplace" -- its first launch outside the US and a product developed entirely in Britain.

Last Tuesday, Google revealed it will add a new office building to a complex currently under development behind London's King's Cross train station.

A total of 7,000 Google staff will eventually be working at the hub, which is set to open in 2018.

Google's chief executive Sundar Pichai told the BBC he would "worry" if controls on skilled migration were made more stringent following Brexit.

He said London was a place "where people are willing to come from anywhere in the world.

"Increasingly, for the kinds of complex things we do, we need to bring people who are across many disciplines -- with many different backgrounds - together to solve problems," he said.

A report earlier this month by Nesta, a British innovation charity, and the European Digital Forum found London was the best city in Europe for digital start-ups, with Stockholm coming in a close second.

The European Digital City Index analysed the 28 EU capitals, weighting cities on scores including business environment and digital infrastructure.

"Government must continue to invest in digital skills and digital infrastructure, as well as addressing the cost of office space," said Chris Haley, Nesta's head of startup and new technology research.

"Of course, it also remains to be seen how a 'hard Brexit' will impact on the UK's business allure for digital startups, given that access to markets is also hugely important."

European leaders have warned Britain that its plans to restrict migration from the European Union while maintaining access to European markets for British companies are incompatible and have warned this will lead to a "hard Brexit".

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