The launch of the James Webb Space Telescope has been put back by at least four days to allow for more checks.

A US space agency statement said an "incident" had occurred during launch preparations that may have caused a sudden vibration in the observatory.

A firm date for lift-off, on an Ariane rocket, would be confirmed following the investigation, Nasa added.

Engineers were in the process of attaching the telescope to its launch adapter - the large ring that will hold it in place atop its rocket - when a securing clamp unexpectedly popped open.

The US space agency statement read: "A Nasa-led anomaly review board was immediately convened to investigate and instituted additional testing to determine with certainty the incident did not damage any components.

"When you work on a $10bn telescope, conservatism is the order of the day.".

The telescope is considered robust.

It has been built to survive the intense shaking and noise when its Ariane rocket climbs away from the launch pad.

If the current investigation finds nothing awry, Engineers will move forward with fuelling the telescope, prior to lifting it on top of the Ariane vehicle about one week before roll-out to the launch pad.