1 of 2 | European High Representative of the Union for Foreign Affairs Josep Borrell said Russia’s decision to remove buoys marking its international border with Estonia was “unacceptable.” File Photo by John Thys/EPA-EFE

Russian border guards on Thursday removed 24 of 50 buoys placed by Estonia on the 48-mile river, marking sailing routes on the international boundary with Russia.

Estonia is a member of the North Atlantic Treaty Organization, and NATO Secretary General Jens Stoltenberg said he spoke with Estonian Prime Minister Kaja Kallas, saying the bloc stands “in solidarity” with the nation “against any threat” to its sovereignty.

The Narva River flows north into the Baltic Sea and is the largest in Estonia in terms of discharge.

The current border was established in 1985.

Earlier in the week, Russia announced it was entertaining a unilateral redrawing of its border in the Baltic Sea. It later deleted the posting without further explanation.

“This border incident is part of a broader pattern of hybrid actions by Russia, including on its maritime and land borders in the Baltic Sea region,” Borrell said.

Russia’s proposal was based on the idea that the nautical charts used to establish the border are now out of use.

“Estonia’s response remains calm and clear-eyed,” the Estonian Ministry of Foreign Affairs said in a statement issued Thursday.

“We treat this as a provocative border incident. We will communicate with the Russian Federation through our border representatives and diplomatic channels that such actions are unacceptable, and demand an explanation about the removal of the buoys and their immediate return.”