U.S. Central Command has seen more "unprofessional" and "unsafe" behavior from Russian pilots in Syria since March 1, a commander said Thursday.

Gen. Michael Kurilla explained the ongoing harassment of U.S. forces in the region at a meeting of the Senate Committee on Armed Services.

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"What we are seeing, though, is an increase recently in the unprofessional and unsafe behavior of the Russian Air Force in the region," Kurilla stated.

The general explained that Russian aircraft have become emboldened to act aggressively toward U.S. bases in a way not typical of an organized military force.

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"They fly over our bases with ground attack aircraft with weapons on them in an attempt to try and be provocative. But really, it's unsafe, unprofessional, not what we expect of a professional air force. They want to try and renegotiate the deconfliction protocols that they violate every day."

Sen. Deb Fischer, R-Neb., asked Kurilla, "This is not new Russia behavior, is it, sir, especially in regard to the drone incident that we have recently seen?" 

"It's not new, but we have seen a significant spike since about 1 March in Syria," Kurilla responded.

The behavior of Russian military aircraft has become a major concern for U.S. defense officials after a fighter jet harassed a U.S. drone and clipped its propeller, sending it crashing into the Black Sea.

Russian ships are at the MQ-9 drone crash site in the Black Sea, a U.S. defense official told Fox News on Thursday. Russia sent vessels to search the debris field almost immediately following the crash.