Increasingly gloomy Russian scientists failed in repeated attempts Thursday to give a vital boost to a pioneering Mars probe that got stuck in a low Earth orbit and now threatens to crash within days.

The unmanned Phobos-Grunt spacecraft lost its course to the Red Planet and its fabled moon Phobos -- a mysterious rock whose name means "fear" in Greek -- after blasting off from Russia's space centre in Kazakhstan early Wednesday.

The setback extended an unprecedented year-long streak of Russian space mishaps and dimmed the once-vaunted programme's hopes of sending a manned mission to Mars some time in the next 25 years.

Jittery scientists went into the mission conceding that it was fraught with risks because Russia had not done anything successful in interplanetary travel since a Soviet-era mission to Venus and Halley's Comet in 1986.

The probe got stuck after its thrusters failed to fire once the craft had reached its initial orbit. But space agency Roscosmos only received the news through outside sources because it had no radar in South America, above which the craft was at the time.

Space officials' mood grew progressively grimmer Thursday as the hours passed and the few moments in which contact with the helplessly spinning vehicle could be established produced only silence on the end of the line.

"The scariest thing in this field is when you get no signal back from the craft," the unnamed source told RIA Novosti after Thursday's second failed attempt to establish contact with the probe.

"The chances of it being revived and sent on its way to Mars are extremely small," another official told the Gazeta.ru website.

The European Space Agency joined Russia's long-distance efforts to rescue the dying craft by enlisting its stations in French Guiana and Australia.

And one glimmer of hope emerged on news that the craft was falling back to Earth slightly slower than initially suspected.

"It is losing two kilometres (6,600 feet) a day," a Roscosmos official told Interfax on customary condition of anonymity. "If this trend continues ... it could stay up for several weeks or perhaps even a month."

But other officials said this may only delay the inevitable because its battery will likely expire by the weekend and leave the craft deaf to outside commands.

"If the (upper-stage) thrusters fail to fire, Phobos-Grunt will soon turn into space junk," the Roscosmos official predicted.

Russia's main concern now is that the 13.5-tonne structure -- also carrying the Chinese Yinghuo-1 satellite it was supposed to place in orbit around Mars -- and its highly toxic fuel could crash back to Earth.

Officials said it was much too early to predict whether the fuel and the ship's other dangerous material would all disintegrate on re-entry should the rescue mission fail.

The five-billion-ruble ($165 million) probe had been set to reach Mars next year before deploying its landing craft for Phobos in 2013. The original plan was to have it return to Earth with soil samples in August 2014.

The mishap caps an inglorious list for Russia's space programme in the 50th anniversary year of Yuri Gagarin's first flight into space.

Three navigation satellites plunged into the sea after a failed launch in December and Russia has since lost new military and telecommunications satellites upon launch.

The accident also comes just five days before Russia is due to resume manned space flights to the International Space Station that ground to a halt in August with the crash of a cargo craft.

"The Mars mission's failure could mean that we lose space as a field of scientific research," the Nezavisimaya Gazeta daily observed.