Two more craters of unknown origin have been spotted in Russia's Siberia region, weeks after a similar-looking hole was found in the isolated northernmost area, a local paper reported.
The Siberian Times, an English-language newspaper, published pictures of two new giant holes found by reindeer herders, one located in the Yamal and the other in the Taymyr peninsula, both above the Arctic circle.
The paper said that theories of their origin ranged from meteorites or stray missiles to aliens or an underground gas explosion. The report could not be confirmed independently.
Russian state television reported this month that a giant hole had appeared in the gas-rich Yamal peninsula where temperatures plummet below minus 50 degrees Celsius and the sun barely rises in winter.
A Russian scientific expedition arrived at the site to inspect the first crater this month, according to a report by state-run Vesti.ru website.
Yamal is one of Russia's richest regions in natural gas.
A meteorite, which weighed about 10 tonnes, hit central Russia last year, injuring more than 1,000 people.
Experts drew comparisons with an incident in 1908, when a meteorite devastated an area of more than 2,000 sq km in Siberia.