Two EU agencies employing more than 1,000 in London will definitely move to the continent, despite UK attempts to keep them after Brexit, officials say.
The British government said this week that their location would be decided during Brexit talks.
But a European Commission spokesman has insisted they should move to the EU.
"The United Kingdom is leaving the European Union and it will have no say in the location of EU agencies," said Margaritis Schinas.
The European Medicines Agency has 897 staff while the European Banking Authority employs 159 people, and the UK's decision to leave the EU has prompted interest from several EU countries in hosting the two highly specialised organisations.
The UK department run by Brexit Secretary David Davis appeared to hold out hope on Monday that the two agencies might remain in London. In a statement it said no decisions had yet been taken and that the two sides would discuss how best to continue co-operating on bank and medicine regulation.
But Mr Schinas said relocating was a consequence of Brexit. "A matter for the negotiations will be the duty for the United Kingdom to facilitate the transfer of these agencies, helping to ease the practical and financial burden for the experts working there who will have to relocate to another city in the EU."
It also emerged that UK Prime Minister Theresa May had spoken to European Commission President Jean-Claude Juncker since her decision to call a general election on 8 June.
The Commission spokesman said "real political negotiations" on Brexit would not start until after the vote.
On 29 April EU government leaders will meet to discuss guidelines proposed last month by Donald Tusk, who heads the European Council.
The UK prime minister formally triggered Article 50 of the Lisbon Treaty and EU officials say they do not expect the election to make any difference to the timing of talks.