MIAMI – Secretary of State John Kerry said Thursday that under U.S. military rules of engagement, the Navy ship that Russian military jets buzzed in the Baltic Sea this week could have opened fire.

The guided-missile destroyer USS Donald Cook reported that pairs of Russian Su-24 attack planes made numerous close-range passes on Monday and Tuesday. The planes appeared to be unarmed. On at least one occasion an Su-24 came within an estimated 30 feet of the Cook, which was in international waters about 70 nautical miles from the Russian enclave of Kaliningrad, which hosts Russian military forces.

The Cook did not respond except to unsuccessfully query the Russian pilots by radio.

In remarks to CNN Espanol in Miami, Kerry condemned the Russian actions and said that “under the rules of engagement” it “could have been a shootdown.”

In all cases a military commander has the authority to defend his or her ship, plane or other unit. The commander is expected to use his or her best judgment under the circumstances to determine whether the ship faces an imminent threat.

White House spokesman Josh Earnest said the U.S. raised its concerns through its military defense representative at the U.S. Embassy in Moscow.