FRANKFURT (Reuters) -Deutsche Bank shares were 5.5% lower in early trade on Monday after news that Germany's largest lender could be on the hook for up to 1.3 billion euros ($1.39 billion) in a yearslong lawsuit claiming it underpaid in its purchase of Postbank.

Deutsche Bank unexpectedly announced late on Friday that it would make a provision to offset possible claims in litigation in the suit.

Deutsche Bank, which said it "continues to disagree strongly" with any view that it underpaid, did not specify the amount it set aside but noted that claims totalled about 1.3 billion euros.

Deutsche had been enjoying the glow of better-than-expected earnings last week and a steep rise in its share price.

It said that the provision would impact its second-quarter and full-year profitability.

($1 = 0.9325 euros)