Denmark on Tuesday raised its cyber security alert level from “medium” to “high” after several attacks by pro-Russian hacker groups in recent weeks, the country’s Centre for Cyber Security said.

“The risk level is being raised on the back of high activity among pro-Russian cyber activists, who are carrying out many attacks against targets within a wide range of NATO countries,” the center said in a statement.

Websites of several institutions and companies in Denmark, including the central bank, commercial banks, ministries and the military, have in the past month been increasingly targeted by so-called distributed denials of service (DDoS), which direct traffic towards targeted servers in a bid to knock them offline.

Pro-Russian hacker groups have on Telegram claimed responsibility for some of the recent attacks on Danish institutions. Moscow has consistently denied that it carries out hacking operations.

Hackers have become better at planning and executing their attacks, giving them more “striking power,” the center said, adding it expects to see more such attacks in the future.

The hackers are “driven by ideological or political motives” which increases the likelihood of attacks in response to isolated incidents such as Quran burnings in front of Turkey’s embassies in Stockholm and Copenhagen, the center said.