Lithuania’s foreign minister, Linas Antanas Linkevicius, said he had tried to get an explanation but had gotten nowhere because Moscow declined even to respond to repeated requests for clarification. Lithuania, he said, lodged a series of formal diplomatic protests but “got no reply.”

The United States is also making its presence felt, and it held its annual naval exercises in the Baltic Sea last week with an unusually large number of ships, aircraft and personnel from NATO countries, including Lithuania, as well as nonmembers like Sweden. Russian vessels shadowed American ships as they left the port in Poland.

The flurry of Russian naval activity along the route of the high-voltage cables also suggests a more targeted agenda. It has sent a blunt warning of Russia’s disquiet over threats to one of its principal geopolitical goals: keeping a firm grip on energy supplies as a powerful political and commercial tool in neighboring territories Moscow would like under its thumb.

With the arrival here in October of a huge floating factory to convert liquefied natural gas from Norway into the burnable variety, Lithuania secured independence from Russia for gas, and it is now pushing on with the undersea cables in the hope that it can do the same for electricity. Lithuania currently imports 60 percent of the electricity it needs from Russia and from its fellow Baltic nations.

On the same morning that the Emanuel reported the arrival of the Russian Navy in the cable zone, the captain of the Alcedo, a second vessel tasked with guarding the seabed cables, reported troubles of its own.

In a message to Rederij Groen, the Dutch company that operates the Alcedo, the captain said a Russian naval vessel had ordered him to clear out of the area until the evening. “Left location and set course to north,” he added.

“When you are a civilian ship and you get told to move by a military ship, you move,” said Daivis Virbickas, chairman of the board of Litgrid, Lithuania’s electricity transmission system operator. The company is sponsoring the cable project in partnership with Svenska Kraftnat, its Swedish counterpart.