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Scientists say the threat of another asteroid strike like the one that hit Russia in February this year is much higher than was previously thought.

Researchers writing in the science magazine Nature say that space rocks of a similar size to the one that exploded over Russia are hurtling into the Earth's atmosphere surprisingly often.

An international team found that in the past 20 years, about 60 asteroids up to 20 meters wide had smashed into the Earth's atmosphere. This number was far more than was previously thought.

Most of them went undetected because they exploded over the ocean or in very remote areas.

This suggests that up until now, experts have underestimated the risk from asteroids of this scale.

The scientists say early warning systems should be put in place that can find when and where these rocks may hit.