VILNIUS (Reuters) – Russian border guards have removed shipping buoys on the Estonian side of the river that separates the two countries, the Baltic state said on Thursday, adding it would demand an explanation and the return of the equipment.

About 24 of the 50 buoys recently placed on the Narva River to mark shipping routes were removed in the early hours of Thursday, Estonian police and border guards said in a statement.

Natural changes in the riverbed make it necessary to re-track shipping routes every year, the agency said. The position of the buoys between Russia and Estonia has been disputed since the large-scale Russian invasion of Ukraine in 2022.

The Russian Defense Ministry briefly published a proposal to redraw Russia’s maritime border in the eastern Baltic Sea earlier this week, but later deleted it from an official portal after it sparked concern among NATO members, including Estonia.

It was not immediately clear whether the removal of the buoys was related to possible Russian plans for a border in the Baltic Sea.

The Estonian Foreign Ministry said it viewed the removal as a provocative border incident and would immediately demand an explanation and the return of the buoys.

“This action by Russia, carried out under cover of night, fits well into the broader pattern of Russia’s provocative behavior, including on its borders with neighboring countries,” it said in a statement.

The Narva River originates from a lake between Russia and Estonia and flows into the Gulf of Finland, part of the Baltic Sea.

The Russian Foreign Ministry did not immediately respond to a request for comment.

Russian Foreign Ministry spokeswoman Maria Zakharova said on Thursday that Russia’s borders on the Baltic Sea must be in line with international law and that the Defense Ministry’s work to clarify the border was of a technical nature.

(Reporting by Andrius Sytas, writing by Louise Rasmussen, editing by Terje Solsvik, Philippa Fletcher, Alexandra Hudson)