A Russian frigate fired two flares towards a Danish military helicopter in international waters off the coast of Denmark, narrowly missing the aircraft on Monday, the Nordic NATO member’s military said.

Axar.az reports, citing Reuters, the Fennec military helicopter had been on a routine mission to photograph the Russian frigate, the Danish defense command said in a statement late on Monday.

One of the flares passed close to the helicopter, it said.

Flares are pyrotechnics usually used as a warning signal at sea.

Denmark’s Foreign Minister Lars Lokke Rasmussen called the incident “unacceptable” and said it could have endangered human lives.

“For our part, Denmark is working to ensure that all shipping can pass peacefully through Danish waters, but Russia is gradually moving the line for what it considers acceptable behavior,” he said in a statement on Tuesday.

He added that he had summoned Russia’s ambassador to Denmark for a meeting.