Four more global banks are being investigated for the alleged financial market manipulation that led to fines of $453 million against Barclays Bank, British Treasury chief George Osborne said on Thursday, causing stocks in those groups to plummet.

Mr. Osborne said Citigroup in the U.S., Switzerland’s UBS, and Britain’s HSBC and Royal Bank of Scotland were also being probed for allegedly providing false figures on key interest rates upon which mortgages and consumer loans are priced.

On Wednesday, U.S and British regulators imposed the fines on Barclays for manipulating the interest rate the London Inter-Bank Offered Rate (LIBOR) to its advantage between 2005 and 2009.

“Banks were clearly acting in concert,” said Andrew Tyrie, a British lawmaker, who is also chairman of the influential Treasury Committee in the House of Commons. “I fear it’s not going to be the end of the story, that we are going to find that other banks have been involved.”

Mr. Tyrie said his committee would summon Barclays chief executive Bob Diamond to explain what happened at the bank.

Though Mr. Diamond has decided to waive his 2012 bonus in the wake of the fines, he’s facing calls to step down. Prime Minister David Cameron, when asked whether Mr. Diamond should resign, said ``he thinks the whole management team have got some serious questions to answer. Let them answer those questions first.”

The massive fines are unlikely to be the end of the pain for Barclays. The cost of lawsuits related to the LIBOR scandal will likely be bigger, said Sandy Chen, banking analyst at Cenkos Securities.

“Since Royal Bank of Scotland, HSBC and Lloyds Banking Group have also been named in lawsuits, we expect they will also face significant fines and damages. We are penciling in multi—year provisions that could run into the billions,” Chen said.

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