Barclays reported a 5 percent fall in first-quarter adjusted pre-tax profit to £1.7 billion ($2.9 billion), as the fixed-income division of its investment bank slowed dramatically.
The bank's interim management statement comes ahead of details of a large-scale reorganization, due on Thursday, in which a major shake-up of its investment banking operations is expected.
Net profit at the bank rose to £965 million for the first three months of the year.
Profits almost halved at its investment bank, which suffered a 28 percent fall in income, after income at the fixed-income, currencies and commodities (FICC) wing plummeted 41 percent. The division is facing job cuts and restructuring in Thursday's announcement.
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Antony Jenkins, chief executive of Barclays, said in a statement: "This plan will address issues underlying the performance challenges we have recently experienced, including positioning the Investment Bank for the new operating and regulatory environment."
The bank confirmed it was "cautious" about the current trading environment and "focused on structurally reducing the cost base in order to improve returns" - a signal that further cuts to headcount are likely.
Jenkins faced shareholder protests at the bank's annual general meeting earlier this month, after investors holding over one third of Barclays shares failed to back the bank's pay policy.
The bank paid out £2.4 billion in bonuses last year, up 10 percent on 2012, despite a one-third drop in profits.
Early signs suggest that bonuses for this year will be lower. Tushar Morzaria, the company's chief financial officer, told reporters Tuesday that fixed compensation, including role-based pay, was down 8 percent in the first quarter for the investment bank.
He added that problems in the FICC division had continued into April.