A Russian fighter jet collided with the rear propeller of an unmanned U.S. military drone in the international airspace over the Black Sea on Tuesday morning, forcing the U.S. to bring the drone down off the coast of Ukraine, U.S. officials said.

The incident, which involved two Russian Su-27 jets, was denounced as "unsafe and unprofessional" by the U.S. State Department. A spokesman called it a "brazen violation of international law" that led to the summoning of Russia's ambassador for a diplomatic meeting in Washington.

Afterward, the ambassador, Anatoly Antonov, insisted that the Russian jets had not hit or fired on the drone, a MQ-9 Reaper.

The Russians claimed Tuesday that the Reaper drone was acting as an "intruder" and flying toward Russia's borders.

U.S. European Command, or EUCOM, labeled the incident as "dangerous" and said in a statement that it could "lead to miscalculation and unintended escalation."

A U.S. official was equally blunt -- telling ABC News that the Russian pilot who hit the drone, seemingly unintentionally, was acting "reckless and juvenile."

"At approximately 7:03 AM [local time], one of the Russian Su-27 aircraft struck the propeller of the MQ-9, causing U.S. forces to have to bring the MQ-9 down in international waters," EUCOM said in its statement.

EUCOM said the incident "demonstrates a lack of competence in addition to being unsafe and unprofessional."

"Several times before the collision, the Su-27s dumped fuel on and flew in front of the MQ-9 in a reckless, environmentally unsound and unprofessional manner," EUCOM added.

The incident is apparently the latest in what EUCOM described as "a pattern of dangerous actions by Russian pilots while interacting with U.S. and Allied aircraft over international airspace, including over the Black Sea."

"Our MQ-9 aircraft was conducting routine operations in international airspace when it was intercepted and hit by a Russian aircraft, resulting in a crash and complete loss of the MQ-9," U.S. Air Force Gen. James B. Hecker, commander of the U.S. Air Forces in Europe and Africa, said in a statement. "In fact, this unsafe and unprofessional act by the Russians nearly caused both aircraft to crash."

"U.S. and Allied aircraft will continue to operate in international airspace and we call on the Russians to conduct themselves professionally and safely," Hecker added.

The unarmed MQ-9 drone had taken off from Romania and was flying at an altitude of 25,000 feet in international airspace southwest of Crimea with its transponder on when it was intercepted by the two Russian fighter jets, a U.S. Air Force official told ABC News.