An unmanned Russian spacecraft on a mission to a Mars moon failed Wednesday to find the right course to the red planet, a potentially devastating blow to Moscow's hopes of resuming planetary exploration.

The Phobos-Grunt probe blasted off successfully from the Baikonur cosmodrome overnight but did not manage to leave its Earth orbit as planned several hours later to go on its planned trajectory for Mars, the Russian space agency said.

Engineers now have two weeks to send the probe out to Mars while batteries last. The loss of the probe would be a disaster for Russia, which has not had a single successful planetary mission since the fall of the Soviet Union.

"I would not say it's a failure. It's a non-standard situation, but it is a working situation," said Roscosmos chief Vladimir Popovkin.

Roscosmos said it would make its first attempt to contact the probe when it entered the zone of radio communications after 11:00 pm Moscow time (1900 GMT) on Wednesday.

The space agency said it had a window of two weeks to reprogramme the probe, after Popovkin initially said that it only had three days.

"A closer analysis of the orbit parameters and fuel supplies on board showed that such commands must be given in the course of two weeks," the agency said in a statement on its website.

The hugely ambitious mission aimed to place the craft in orbit around Mars, land a probe on the surface of its largest moon Phobos, scoop up soil and bring the first ever sample of the Martian satellite back to Earth.

The probe is also carrying a Chinese satellite, Yinghuo-1, which is supposed to go into orbit around Mars in a landmark space cooperation between Moscow and Beijing.

Popovkin said the probe's motors had failed to fire twice to orientate it on a course for Mars and it was still carrying the fuel that would have been used in this manoeuvre.

Engineers will now race against the clock to re-programme the probe to set it off on the right trajectory to Mars.

Even ahead of launch, Popovkin had admitted the mission was a "risk", saying that 90 percent of the craft consisted of completely new equipment as Russia had done almost nothing in planetary exploration for 20 years.

The probe will be impossible to save if the problem proves to be a defect rather than simply a programming error, a source in the Russian space industry told the Interfax news agency.

"It could turn out the reason for the abnormal situation was damage or the malfunctioning of some equipment. In this case it will be impossible to save the probe in any way."

Interfax said the probe was insured for 1.2 billion rubles (40 million dollars) but noted that insurance was becoming trickier for Roscosmos after a string of failed missions in the last year.

Three navigation satellites plunged into the sea after a failed launch, a new military satellite was lost in orbit while a supply ship bound for the International Space Station crashed into Siberia.

Moscow was desperate to show it could be a superpower in space exploration and was still inspired by the daring spirit of first man in space Yuri Gagarin, in the year it celebrated the 50th anniversary of his historic voyage.

But Phobos-Grunt was also haunted by the apparent jinx of the Soviet Union and Russia's past botched attempts to explore Mars and its two moons.

The Soviet Union sent up a string of probes but most failed in their missions, at a time when NASA was able to impress the world with the stunning images of Mars from its successful Mariner and Viking probes.

Post-Soviet Russia endured one of its most humiliating space failures in November 1996 when its Mars-96 probe broke up after launch in a disaster that appeared to symbolise the disintegration of the Russian space programme.

Stung by that catastrophe, Russia has not attempted a single planetary mission since. Moscow's last successful voyages were the Vega 1 and 2 probes of 1986 in the Soviet era which explored Venus and Halley's Comet.

Igor Lisov, editor-in-chief of the specialist journal Novosti Kosmonavtiki (Space News) said there was still a chance of saving Phobos-Grunt.

But he said it had always been a risk after Russia's long absence from planetary exploration "to send up a super complex project" that Roscosmos itself said was not perfect but simply could not be delayed any longer.

If all still goes to plan, Phobos-Grunt would reach Mars next year and then deploy its lander for Phobos in 2013, scooping a chunk of its surface before returning the sample back to Earth in August 2014.

Phobos, which orbits Mars at a radius of just under 10,000 kilometres, is believed to be the closest moon to any planet in the solar system and scientists hope it will reveal secrets about the origins of the planets.