Sensitive defense documents containing details about the British military have been found at a bus stop in England, the BBC reported Sunday.

The papers included plans for a possible U.K. military presence in Afghanistan, as well as discussion about the potential Russian reaction to the British warship HMS Defender’s travel through waters off the Crimean coast last week, the BBC said.

The broadcaster said a member of the public who wanted to remain unnamed contacted it when they found the pile of documents — about 50 pages in all — in a soggy heap Tuesday behind a bus stop in Kent, southeast of London.

The Ministry of Defense said an employee had reported the loss of the documents last week.

“The department takes the security of information extremely seriously and an investigation has been launched,” it said in a statement. “It would be inappropriate to comment further.”

The HMS Defender upset Russia’s military on Wednesday when it sailed south of the Crimean Peninsula in a Black Sea area that Moscow claims as its territorial waters. Many nations, including the U.K., do not accept Russia’s 2014 annexation of Crimea from Ukraine and consider that area to be Ukrainian waters.

Russia said one of its warships fired warning shots in response to the destroyer’s intrusion, but Britain denied that account and said the warship was not in Russian waters. The U.K.’s Ministry of Defense said the ship was “conducting innocent passage through Ukrainian territorial waters in accordance with international law.”