An asteroid the size of a mountain is heading in the direction of Earth, and although it's not seen as posing any immediate threat it will need to be closely monitored, scientists say.

The asteroid dubbed 2014 UR116, discovered by a Russian research team, crosses the Earth's orbit every 3 years, says team leader and astrophysicist Vladimir Lipunov.

The fact it has only recently been discovered should be taken as a warning that increased efforts should be made to track such large asteroids, he says, because its path could be changes by the gravitational pull of other planets as it travels through the solar system.

"We need to permanently track this asteroid, because even a small mistake in calculations could have serious consequences," he says.

The asteroid was discovered on October 27 by the  MASTER-II observatory in Kislovodsk, Russia.

Despite some speculations, mostly in Russian news media, that it could represent an impact threat, "it does not represent a threat because its orbital path does not pass sufficiently close to the Earth's orbit," NASA's Jet Propulsion Laboratory in Pasadena, Calif., said in a release.

Astronomers, noticing its orbit was the same as an object observed 6 years ago, combined those observations with the new ones to predict its future motion.

The predictions, yielded by automatic computations using the Sentry system at NASA's Near-Earth Object Program Office at JPL, rule out 2014 UR116 as in impact threat for at least the next 150 years, the astronomers say.

The office maintains a website where scientists, the public and the media can verify information about asteroid discoveries and possible risks of impacts, JPL said.

A consortium of European research institutions maintains a similar website, the Near Earth Objects Dynamic Site.

Asteroids and comets that can approach the Earth's orbit to within about 28 million miles are considered near-Earth objects, or NEOs.

NASA, which maintains a catalog of all NEOs, says it has found and identified almost 900 such objects of at least a kilometer in diameter.

However, NEOs can range in size from as small as a few feet to as large as 1036 Ganymed, the largest NEO found to date at 25 miles in diameter.

"The first near-Earth object was discovered in 1898," says Don Yeomans, long-time manager of the Near-Earth Object Program for JPL. "Over the next hundred years, only about 500 had been found. But then, with the advent of NASA's NEO Observations program in 1998, we've been racking them up ever since. And with new, more capable systems coming on line, we are learning even more about where the NEOs are currently in our solar system, and where they will be in the future."