European Union antitrust regulators will unconditionally approve a $19 billion offer by Facebook, the world's most popular social network, for mobile messaging startup WhatsApp, two people familiar with the matter said on Thursday.

The landmark deal, the largest in Facebook's 10-year history, will give the company a strong foothold in the fast-growing mobile messaging market and pit it against telecom companies.

"It's unconditional clearance," one of the people said, declining to be named because the decision by the European Commission is not yet public.

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