A Russian military satellite which parked itself between two US Intelsat satellites did not put them at risk, a Russian space expert says.
Ivan Moiseyev, head of Russia's Space Policy Institute, said he understood US concerns about the Luch relay satellite's manoeuvres.
"But the possibility of a collision or some kind of interference is extremely small," he was quoted as saying.
Intelsat said it had tried and failed to contact the satellite's operator.
"Despite direct and indirect inquiries by the appropriate regulatory bodies and governmental agencies, the operator of the other satellite was unresponsive," it said in a statement to the BBC.
Intelsat Inc. operates about 50 satellites, some of which are used by the US military, including for drone missions and communications with "remote military outposts".
Lt-Col Tom Crosson of the US Department of Defense said the US military's space command, JFCC-Space, had contacted Russia about the satellite.
"JFCC-Space has transmitted emergency close approach notifications to Russia, based on predictions of a close approach with another space object of 5km (three miles) or less within 72 hours," he told the BBC.
"I understand that there have also been communications between the private operators," he added.
The satellite is being tracked on the website www.space-track.org, where it is described as "Luch (Olymp)". It was launched in September 2014.
According to Mr Moiseyev, "there were no violations in this case".
The Luch, he said, "is simply a relay satellite, sending signals from spacecraft to Earth, for example from the International Space Station (ISS) - we have communications problems there - and from one satellite to another".
"In no way can it be an 'aggressor'," Russia's RIA Novosti news agency quoted him as saying. "Any satellite can make some clumsy manoeuvres - but collisions are extremely rare."
Mr Moiseyev said there had been just one previous incident when an old Russian satellite and a US satellite had collided by accident.
The Space Policy Institute - set up by government bodies in 1993 - is described on its website as an "independent research organisation".
A US space expert, Brian Weeden, tracked the Luch satellite and said it moved to a position in June where there were no other Russian satellites, but which put it "right in between two operational Intelsat satellites... where it remained until mid-September".
At one point it came within 10km of one of those satellites, which is very close in space terms.
Then the Luch began drifting again, Mr Weeden reported in an article in The Space Review.
He said the Luch was not registered with the UN Office of Outer Space Affairs and "there is also a lot of uncertainty about the mission".
What's it doing?
The "Luch" name, used by Russian state media, may also be inaccurate, Mr Weeden said.
"They gave it that name, but it's not that type," he told the BBC by phone.
"Luch" is used for a different class of Russian relay satellites which are in low-Earth orbit, he explained.
But the mysterious activity took place much higher - about 36,000km above the equator, in a type known as geosynchronous orbit (GEO).
"It's now parked next to another Intelsat satellite," he said.
When asked if it could have intercepted Intelsat data he said simply "I have no idea". But he added: "there was no danger of collision".
In an interview with Space News earlier this month, Intelsat General's president Kay Sears said there had been no interference with Intelsat's operations.
The manoeuvres are called rendezvous and proximity operations (RPO), and the US has experimented with them for about 15 years, but now "the Russians and Chinese are catching up", Mr Weeden said.
He described the Russian RPO activities as "very similar in nature to US RPO capabilities".
Plea for openness
BBC space technology expert Jonathan Amos says RPO can be used for spying or anti-satellite missions, but also to recover and repair a broken satellite or to clear some satellite junk out of orbit.
But it requires all parties to be clear and open about what they are doing in orbit, our correspondent added.
Intelsat said it had "contacted the appropriate regulatory bodies and governmental agencies to express our concern and to ask them to reach out to the operator to correct the situation".
Intelsat urged information-sharing through the Space Data Association (SDA), "whose mission is to enhance 'safety of flight' for satellite operators globally".
Update, 22 Oct 2015: The story was updated after Lt-Col Tom Crosson at the US Department of Defense told the BBC that the US military had transmitted "emergency close approach notifications" to Russia.