Citigroup Inc. said a cyber attack in May affected almost twice as many accounts as the bank’s figures had initially suggested, as major U.S. lenders come under growing pressure from lawmakers to improve account security, Reuters reported.

A total of 360,083 North American Citigroup credit card accounts were affected by the breach, Citigroup said in a statement released late yesterday.

Of those affected, some 217,657 customers were issued new cards along with a notification letter, while the remaining accounts were either inactive or had already received new cards earlier, the bank said.

Citigroup had earlier said that about 1 percent of its North American accounts were affected. The bank has about 21 million customers, according to its annual report, and ranks as the third-largest U.S. bank by assets.

The original estimate of the number of affected accounts was “mainly due to the actual number of accounts being more than what’s in the 2010 annual report as well as variances such as some of the accounts being closed,” Citi spokesman Sean Kevelighan said in an emailed response.

Customers’ names, account numbers and contact information were accessed, but Citi said that “data critical to commit fraud was not compromised” and that other consumer banking online systems were not accessed.