Flight tracker highlights US spy plane over empty Ukrainian airspace

According to flight tracking site Flightradar24, two US spy planes have travelled on regular missions from the Mediterranean Sea to Ukraine over the past month.

While Ukraine's airspace has been largely empty amid the crisis with Russia, a remotely piloted US military vehicle called the RQ-4 Global Hawk has flown over the country in circles for hours at a time.

Over the past month, two of the spy planes have travelled on regular missions from the Mediterranean Sea to Ukraine, where they have navigated in repeated loops in the north and the east, according to Flightradar24.

The drones' high-altitude, long-distance flights have coincided with a military build-up by Russia along the Ukrainian border and a flurry of diplomacy among leaders of the United States, Europe and Russia to avert war.

At times, the two planes - under the call signs Forte10, Forte11 and Forte12 - have been the only active aircraft publicly visible over eastern Ukraine. Aviation watchers have taken note, speculating that the United States is making its presence known in a show of force.

"With these types of flights, leaving the transponder on is a conscious decision," said Ian Petchenik, communications director at Flightradar24.

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The US Air Force declined to comment on the details of the flights but said the United States routinely operates aircraft in support of intelligence objectives.