The head of UBS said in a statement that he would not be participating in any merger discussions with either of the two banks.
“We will not participate in any discussions with any company that is contemplating or currently pursuing any merger or acquisition, and we will vigorously oppose any such proposal,” UBS chief executive John Cryan said.
Citi and HSBC, the two largest U.S. financial institutions, have been discussing the potential merger.
Citing “industry-specific information,” Citi said on Tuesday that it had not received any such proposals.
Reuters reported on Wednesday that UBS and Citi had discussed a deal that would combine the two.
The U.K.-based bank has been a strong critic of the financial sector, particularly the investment banks that it controls.
In May, it said it was delaying the opening of its next U.N. headquarters to allow for the consolidation of the U.KS-based bank with the UBS unit.
It has also been a major backer of candidates for the Democratic nomination for president.
The bank has also faced criticism for its role in the global financial crisis, including its role as one of the main lenders to Lehman Brothers Holdings Inc., which collapsed in 2008.