(Reuters) - Time experts were deadlocked on Thursday over whether to scrap "leap seconds" which are occasionally added to clocks to stop them running ahead of the sun.

Delegates from some 100 countries failed to agree whether to call time on leap seconds, which were introduced in 1972 to help real time - measured by the earth's rotation on its axis and around the sun - 'catch up' with atomic time.

Natural time fluctuates almost imperceptibly due to the earth's irregular rotation, tides and earthquakes.

Thirty four seconds has had to be added in the past 40 years to keep up with atomic clocks which are used in the world's most accurate clocks and computer systems. The United States wanted to scrap the practice but Britain, Canada, Germany and China all opposed the U.S.-led move.

With no agreement, around 700 delegates from the International Telecommunications Union meeting in Geneva agreed to shelve the decision until 2015, avoiding the need for a rare vote.

The U.S. initiative, also backed by France, was based on concerns over possible glitches following adjustments to software used in satellites and navigation systems.

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