A series of suspicious fires have recently been reported in European countries that support Ukraine. Those nations are on high alert as they suspect Russia is carrying out "hybrid attacks," or attempts to cause disruption without using military force.

In Poland's capital Warsaw, a fire destroyed a shopping center with more than 1,400 stores in May.

Polish Prime Minister Donald Tusk said, "There is a high possibility that Russian intelligence agencies were behind the fire."

Tusk said nine people were detained on suspicion of committing arson and other acts of sabotage under orders from Russia.

He suggested they may also have been involved in a fire in another shopping center in Lithuania just before the Warsaw incident.

US Secretary of State Antony Blinken has confirmed Russia's involvement. He said the Kremlin has been intensifying its hybrid attacks against NATO member states.

There is speculation that Russia is using new tactics to carry out hybrid attacks.

Last month, someone attempted to set fire to vehicles at a bus depot in the Czech Republic capital, Prague.

A man from South America was indicted over the incident. Police say the suspect was paid for committing the crime and he has no links with any terror group or criminal organization. Local media reported the man had received 3,000 dollars.

Michal Koudelka, the head of Czech Security Information Service, the intelligence agency investigating the case, told NHK that the suspect had received instructions from a Russian intelligence agency through people on social media. But Koudelka says the suspect did not know he was acting on behalf of Russia.

NATO member countries said at their recent summit that Russia is intensifying hybrid attacks that "constitute a threat to their security." They affirmed they will counter the threat by maintaining close coordination.