THE HAGUE, Netherlands (AP) — Pro-Russian hackers launched a series of denial-of-service attacks Monday on several municipalities and organizations linked to a NATO summit this week in the Netherlands, the Dutch government announced.

The National Cybersecurity Center said in a statement that many of the attacks were claimed by a pro-Russian hackers’ group known as NoName057(16) “and appear to have a pro-Russian ideological motive.” It did not elaborate.

The cybersecurity center said it was investigating the attacks that flood a site with data in order to overwhelm it and knock it offline, and was in contact with “national and international partners.”

Raoul Rozestraten, a spokesman for the municipality in The Hague, the Dutch city hosting the summit Tuesday and Wednesday, said the attacks hit municipalities around the country.

“We noticed more traffic on the website of some of our service providers,” he told The Associated Press. “As of now, everything in The Hague is working normally.”

The government had launched a major security operation, named “Orange Shield,” around the NATO summit.