More websites of the nation's biggest banks are bogging down.

Both PNC Financial Services Group (PNC) and U.S. Bancorp (USB) said Wednesday that customers encountered delays when trying to bank online, bringing to at least five the number of financial institutions that have experienced Internet slowdowns since a cyber-threat against American banks emerged last week.

JPMorgan Chase (JPM) said its websites also slowed again Wednesday, about a week after the bank first reported glitches. Customers of Wells Fargo (WFC) met with hang ups as well this week when they tried to transact electronically.

"The issues are clearly related to unusual and coordinated high-traffic volume designed to slow down the system," US Bancorp spokesman Tom Joyce told American Banker. "This is very similar to what other banks have experienced in the past week."

PNC spokesman Fred Solomon told American Banker the bank "is aware that some customers could not access PNC's Web site on the first attempt today."

Both banks said they were working to restore service fully.

"We are receiving reports that some of you may be unable to access Chase Online — we are investigating and will keep you updated," Chase tweeted Wednesday. The bank later told customers the site was working and apologized for the inconvenience.

The slowdowns come amid threats by a group that has vowed to wage a cyber-offensive against U.S. financial institutions in retaliation for the "Innocence of Muslims," an American-made, anti-Islamic film. "These series of attacks will continue until the erasing of that nasty movie from the Internet," a group named Cyber fighters of Izz ad-din Al qassam posted recently on, a website used by computer programmers.

"I won't speculate about where the attacks are coming from, but they seem to be pretty well coordinated," Jeff Herdell, founder of, which tracks website outages, told American Banker.

Bank of America said last week a digital deceleration mired some of its customers, although the bank later said service resumed normally.

The snags also follow a report by Reuters that hackers from Iran may have targeted the biggest U.S. banks as part of a broader cyber offensive against the United States. Iran says it is not coordinating the attacks. "Iran has not hacked the U.S. banks," Gholam Reza Jalali, head of Iran's Civil Defense Organization, told the FARS News Agency on Sunday.

The Financial Services Information Sharing and Analysis Center, an industry group, has raised its cyber threat level to "high" from "elevated" and urged members to monitor their networks carefully. The FBI warned recently that thieves may be trying to steal information from financial firms' websites that could be used to make fraudulent wire transfers.