NEW YORK — U.S. Bancorp customers were experiencing intermittent delays with the institution’s website and online operations on Wednesday, spokesman Tom Joyce said. The Minneapolis bank was experiencing unusually high Web traffic and coordinated attacks “very similar” to what other major banks have experienced in the past two weeks, he said. Wells Fargo & Co.’s website was attacked Tuesday.

A computer security expert blamed massive denial of service attacks, in which perpetrators overwhelm computer servers with communications demands, causing networks to seize up or slow down.

In a posting at Pastebin.com, a group claimed responsibility for last week’s outages at Bank of America, Citi, and JPMorgan before hitting U.S. Bancorp and Wells Fargo. It said it would attack U.S. Bancorp on Wednesday and PNC Financial Services on Thursday.