PNC (PNC) on Thursday rode out a slowdown of its online banking service that left some customers unable to log in to their accounts.

The Pittsburgh-based bank took to Twitter in the morning after some customers complained of being unable to reach the company's website.

PNC attributed the bogging down to "certain internet service providers," according to a status message the company posted online Thursday afternoon.

Company officials said the delays were not the result of a cyberattack. "We did have some access issues that were isolated to certain customers who were in a certain geographic location of some ISPs," said PNC spokeswoman Marcy Zwiebel, who declined to identify the providers.

Because some customers had difficulty accessing their accounts, the bank "wanted to make sure they had information about what was happening," Zwiebel added.