WASHINGTON (Reuters) - Hackers disrupted service over the weekend of a Baltimore computer network that supports emergency calls, forcing the city to resort to manual operations to handle calls, the city mayor’s office said.

A “limited breach” affecting Baltimore’s computer-assisted dispatch system, which is used to support and direct 911 and other emergency calls, was identified Sunday morning, according to Frank Johnson, Baltimore’s chief information officer.

The disruption was the second cyber attack on a major U.S. city within the past week, coming days after Atlanta was struck by a widespread “ransomware” cyber extortion attack that interrupted bill collection services, downed the airport’s wireless internet and impeded other city services.

Some Atlanta city services remained offline for a seventh day following last Thursday’s ransomware attack.

Atlanta police said that some parts of the department’s operations remained impacted by the attack, though its ability to respond to emergencies had not been affected.

“As teams diligently work to restore our network, it would not be prudent right now to go into specifics about police operations,” department spokeswoman Lisa Bender told Reuters. “We have begun to do some tasks manually, and continue to look for other ‘workarounds’ so that we can continue to serve the public with the same level of service they have come to expect.”

City workers turned away residents trying to pay their water bills and attend scheduled traffic court hearings, saying the cyber attack had halted work at those departments.

A senior U.S. cyber security official told Reuters there were no indications the Atlanta attack was related to the one in Baltimore.

During the Baltimore outage, details of incoming callers seeking emergency support could not be electronically relayed to dispatchers, forcing call center staff to do so manually, Johnson said.

The impacted computer was isolated and taken offline and the computer-assisted dispatch system was fully restored by early Monday morning, he said.

“These critical services were not impacted nor disrupted at any time,” Johnson said in a statement.

A spokesman for the mayor’s office declined to say if the city had identified any suspects behind the breach, if any data was stolen or if other city services had been recently targeted in cyber attacks.

An FBI spokesman told the Baltimore Sun that the bureau was providing technical assistance. The regional FBI office in Baltimore could not immediately be reached for comment.