The US bank Citigroup, which employs 9,000 people in the UK, has told staff it would have to move operations out of its hubs in London and Belfast in the event of Brexit.

The announcement follows a warning last week by Citi’s rival JP Morgan that 4,000 jobs could be lost if the UK voted to leave the EU.

Citi’s UK boss, James Bardrick, told staff in an email that a vote to sever links with Brussels would have implications for the business.

“Ahead of the referendum, we have been carefully reviewing the situation and contingency planning around a number of areas, including our organisational footprint and where we book business,” he said.

“A vote to leave the EU is likely to have implications for our UK operations. To continue to serve our clients and maintain efficient access to those markets currently enabled through the EU passporting regime, we would likely need to rebalance our operations across the EU,” he added, without being specific about jobs.

He highlighted the UK’s position as a global financial centre and cited its links to the EU single market as a reason for having operations in London.

“The efficient movement of talent between EU member states is also important to Citi, and many of our clients, whether it be EU nationals from other countries working in the UK or UK citizens working for Citi in one of the other 20 EU countries where we operate,” he said.

Bardrick said the email had been sent because the bank was receiving an increasing number of queries about what the outcome of the 23 June referendum would mean for the organisation, its clients and UK-based employees.

His warning came as the European Central Bank said it was ready to take steps to stabilise markets in the event of any turbulence caused by Brexit.

“The ECB is prepared for all possibilities, as it always has been in this sort of situation, to stabilise markets especially by providing liquidity,” Benoît Cœuré, an executive council member at the bank, told France 24.