Short-selling in shares of First Bank System Inc. jumped 64.8% in the month ended May 15, while it fell at most other banks.

Wall Street observers said the increase may be related to the Minneapolis banking company's own share repurchase activity or to speculation that First Bank will unveil an acquisition soon.

Limited Time Offer

Save $400 off your subscription. Special offer ends April 30, 2017.

14-Day Free Trial

No credit card required. Complete access to articles, breaking news and industry data.