Three man team probing the discovery is now 'missing in tundra', say Emergency Ministry officials.
The team from the Russian Academy of Sciences used a satellite phone to report the discovery of an 'unidentified object resembling a space capsule' in one of dozens of craters to have been discovered recently on the remote Yamal peninsula in Arctic Russia.
The scientists said the grey-coloured object was made of a metal 'unknown on Earth'. They reported a 'hostile environment' at the 48 metre deep crater but did not give further details before their call was cut.
Experts from a leading Siberian university also requested an emergency evacuation from the crater site after an unexplained fault with their helicopter.
'At this moment their call ended, and we could not reach them again. When we sent a back-up helicopter to the site there was no sign of the three-man team,' said a spokesman for the Emergencies Ministry.
'They have vanished. The crater was empty. Searching will continue throughout 1 April.'
Rescuers 'do not exclude that the men have been kidnapped'.
The team had been investigating the cause of the mystery craters, and were taking detailed measurements at the site.
Until now it was assumed the the mysterious holes appearing in Yamal were caused by methane explosions resulting from the release of gas by melting ice.
Other theories were that they were caused by meteorites, or stray rockets. Another version was that holes were dug by humans as a hoax.
Archeologists discovered a new stone bracelet, two sharp pins, a marble ring and fox tooth pendants.
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