The Swedish military, late on Sunday, released a photograph of what it claims to be a “foreign submarine” in the Baltic Sea, off the Stockholm archipelago. It also said, in a statement released along with the photograph, that “several credible sightings” of “strange underwater operations” had been made since Friday.

“Very credible observations have been made at three locations,” Rear Admiral Anders Grenstad, deputy director of operations for the Swedish armed forces, said, in the statement. “The Armed Forces have moved the operation area slightly southward but magnitude of the operation remains undiminished.”

The Swedish military has been searching the Baltic Sea since Friday, following “credible information” about foreign underwater activity in the region.

He also added that the military’s assessment was based on “several observations over the years in the same area…this area is of interest to a foreign power.” He, however, did not specify what the observations were and whether the suspected submarine was a Russian vessel.

“From the information currently available to the Armed Forces, we cannot reach the conclusion that it is a damaged Russian submarine,” Grenstad said.

Svenska Dagbladet, a Swedish newspaper, had claimed on Saturday that intelligence officials had picked up a distress call on a frequency used by Russians, leading to speculation that a Russian vessel was present in Swedish waters.

Russia, however, denied the allegations, stating that its submarines and warships “are fulfilling their duties in the world ocean waters in accordance with a plan,” according to media reports.

“There are no extraordinary, let alone emergency, situations involving Russian warships,” an unnamed Russian defense ministry spokesperson reportedly said on Sunday.