A Russian jet conducting an observation flight over the U.S. stopped for one night at Robins Air Force Base Thursday.

But it's all legitimate, according to the base.

They say the flight is authorized by the 2002 Open Skies treaty, which allows the U.S., Russia and 32 other countries to conduct unarmed observation flights.

One reason for the flight is to verify compliance with arms control agreements, according to an email from base spokesman Roland Leach.

Newsweek reported this week that the jets used in Open Skies must be unarmed. But they may use certain types of electronic surveillance equipment, including "optical panoramic and framing cameras, video cameras with real-time display, infra-red line-scanning devices and sideways-looking synthetic aperture radar."

The flight has to follow a fixed route that's set in advance, Newsweek said. And U.S. and Canadian officials ride along on the two-day flight to ensure that the Russians are following procedures.

Pravda reported this week that the U.S. and the Czech Republic conducted their own Open Skies tour of Russian this week, using a OC-135B.

Leach said the Russian aircraft left Robins Friday morning.

He referred further questions on the visit to the Department of Defense's Defense Threat Reduction Agency.