The Philadelphia Inquirer experienced the most significant disruption to its operations in 27 years due to what the newspaper calls a cyberattack.

The company was working to restore print operations after a cyber incursion that prevented the printing of the newspaper's Sunday print edition, the Inquirer reported on its website.

The news operation's website was still operational Sunday, although updates were slower than normal, the Inquirer reported.

Inquirer publisher Lisa Hughes said Sunday "we are currently unable to provide an exact time line" for full restoration of the paper's systems.

"We appreciate everyone's patience and understanding as we work to fully restore systems and complete this investigation as soon as possible," Hughes said in an email responding to questions from the paper's newsroom.

The attack was first detected when employees on Saturday morning found the newspaper's content-management system was not working.

The Inquirer "discovered anomalous activity on select computer systems and immediately took those systems off-line," Hughes said.

The cyberattack has caused the largest disruption to publication of Pennsylvania's largest news organization since a massive blizzard in January 1996, the Inquirer reported.

The cyberattack precedes a mayoral primary election scheduled for Tuesday. Hughes said the operational disruption would not affect news coverage of the election, although journalists would be unable to use the newsroom on election night.

Hughes said other Inquirer employees will not be allowed to use offices through at least Tuesday, and the company was looking into coworking arrangements for Tuesday, the Inquirer reported.

An investigation was ongoing into the extent and specific targets of the attack, and the company has contacted the FBI, Hughes said.

The FBI in Philadelphia declined to comment in response to questions from Inquirer journalists, the newspaper reported.