BERLIN (Reuters) - Serbian and U.S. paratroopers will jump side-by-side during a joint exercise aimed at strengthening military ties with Serbia, the U.S. general in charge of NATO’s Allied Air Command said, a move that could trigger protests from Moscow.

FILE PHOTO: U.S. Air Forces in Europe Commander Tod D. Wolters speaks during NATO Baltic air policing mission takeover ceremony in Siauliai, Lithuania August 30, 2017. REUTERS/Ints Kalnins

In the exercise, which is taking place at the invitation of the Serbian government, paratroopers from both countries will jump side-by-side from 2 C-130J transport planes built by Lockheed Martin Corp in a so-called insertion exercise.

About 100 U.S. Air Force and U.S. Army personnel will participate in the event, General Tod Wolters, who also oversees U.S. Air Forces in Europe and Africa, told Reuters.

“They will actually get their paratroop wings as a result of these activities. These are confidence-building activities - relationships that will last for a lifetime. And they will certainly enhance the technical expertise of the Serbs,” he said.

It was not immediately clear how many Serbian forces would participate.

Wolters said tensions in the Balkans remained a challenge for NATO and the U.S. military, but engagement was key.

“It will continue to be a challenge, but we’ve got the right command focus. We’ve got the right resources. We’ve got the right dialogue and time will tell what unfolds,” he said.

Any NATO-related activities in Serbia are a red flag for Russia, which worries about NATO expansion in the former communist east.

Moscow has also sought to bolster military ties with Belgrade with the donation of six MiG-29 fighter jets.

Serbia has been performing a delicate balancing act between Russia and the West, rejecting calls by U.S. officials to pick a side.

The largest of the states to emerge from the collapse of Yugoslavia in the 1990s, Orthodox Christian and Slavic Serbia has natural affinity with Moscow, but it is keen to join the European Union.

Although the EU is Serbia’s single largest trade partner and investor, Russia controls its oil and gas supplies.