Editor's note: This story was originally published April 13, 2016, at 11:23 a.m. EST.
In one of the most aggressive actions in recent memory, Russian warplanes conducted "simulated attacks" on the a U.S. Navy vessel in the Baltic Sea on Tuesday, repeatedly flying within 30 feet of the ship, according to a defense official.
Sailors aboard the destroyer Donald Cook said the aircraft flew low enough to create wake in the sea waters surrounding the ship, and the ship's commanding officer said the incident was "unsafe and unprofessional," the defense official said.
"This was more aggressive than anything we've seen in some time," according to the defense official, who spoke on condition of anonymity because U.S. officials have not officially disclosed the incidents.
Sailors aboard the ship described the Sukhoi Russian Su-24 as "wings clean," meaning there were no visible bombs or armaments on the aircraft, the defense official said.
The nature of the overflight as a "simulated attack" may violate a 1973 treaty between the U.S. and Russia that specifically prohibits this type of maneuver, the defense official said.
The maneuver "simulated attack" was one of several aggressive moves by Russian aircraft on Monday and Tuesday.
Shortly after leaving the Polish port of Gdynia, near Gdansk, on Monday, the Donald Cook at was sea in international waters conducting flight operations with a Polish helicopter, part of routine joint training exercises with the NATO ally.
During those flight operations, a Russian Sukhoi Su-24 combat aircraft appeared and conducted about 20 overflights, coming within 1,000 yards of the ship at an altitude of about 100 feet, the defense official said. In response, the commander of the Donald Cook suspended flight operations.
On Tuesday, the Donald Cook was underway in the Baltic Sea when a Russian helicopter — a Ka-27 Helix — made seven overflights and appeared to be taking photographs of the U.S. Navy ship, the defense official said.
Shortly after the helicopter left the area, an Su-24 began making "very low" overflights with a "simulated attack profile," the defense official said. The aircraft made a total of 11 passes overflights.
The ship's commander of the ship repeatedly tried to make radio contact with the Russian aircraft but received got no response, the defense official said.
The ship’s commander reported the incident as "unsafe and unprofessional." After a formal investigation, the incident may prompt the U.S. government to formally lodge a complaint — or "demarche" — with Moscow, the defense official said.
While Russian aircraft during the past couple of years have conducted numerous aggressive overflights that Navy officials deemed "unprofessional," the incident on Tuesday was the first to be deemed "unsafe," the defense official said.
In 1973, the United States and the Soviet Union signed a treaty aimed at preventing the prevention of incidents at sea. That treaty specifically prohibits " simulating attacks," according to the U.S. State Department’s website.
The aircraft likely came from a Russian military installations in Kalingrad, an enclave of Russian territory on the Baltic Coast nestled between Poland and Lithuania.