Bank of Montreal, Canada's fourth-biggest lender by assets, said on Tuesday it had amended its regulatory capital ratios for the first three quarters of 2016, a move that left the bank holding more risky assets than it had reported.

BMO said the "correction" resulted from a recalculation of some of its Basel I components. Basel I rules require banks to hold a certain amount of capital to minimize credit risk.

Canaccord Genuity analyst Gabriel Dechaine estimated that BMO's third-quarter risk-weighted assets, reported at about $260 billion, would likely be inflated by about $12 billion as a result of the restatement.

Barclays analyst John Aiken said the bank would be able to increase its Common Equity Tier 1 (CET1) ratio through internally generated capital.

"This will likely mean lower than previously anticipated dividend growth and no share repurchases for the foreseeable future," Aiken wrote in a client note, while adding that the action would not affect Barclays' long-term outlook for BMO.

BMO said its net income, shareholders' equity and CET1 would remain unchanged for the three quarters.

The company restated its Basel III CET1 ratio for the third quarter to 10 percent from 10.5 percent. The second quarter ratio was reduced to 9 per cent from 10 percent and that for the first quarter to 10.0 per cent from 10.1 per cent.

The bank's shares were down 1.6 per cent at $84.45 in midday trading.