Russia's northern NATO neighbors are tightening security around dams, power plants and natural gas infrastructure in a sign of mounting concern that Moscow will stage a "false flag" attack on them using Ukrainian drones, Reuters reports.

Lithuania said last week that Moscow is considering such a staged attack and Poland, Latvia and Estonia have also warned of acts of sabotage to test NATO's response at a time when U.S. commitment to the Western military alliance is in question.

Kremlin spokesman Dmitry Peskov last month said warnings of Russian clandestine attacks are "scare stories" used to justify militarization against Russia.

Poland and the three Baltic states, which all border Russia and have already found Ukrainian drones on their territory, are taking no chances.

"We are not naive, we see the information, we read between the lines and we are doing our homework," Lithuanian Defense Minister Robertas Kaunas told Reuters.

Another source, an official from the region, said a spate of warnings from "allied intelligence" about Russian activity had made an "overwhelming impression" on the Baltic states but attacks could take place "between today and never."

In Poland, the top oil and gas company Orlen is analyzing alternative gas import routes in case the usual ones are compromised, a person familiar with its operations said.