The launch of Nasa's Dawn space probe, which will explore the Asteroid Belt between Mars and Jupiter, has been delayed until Sunday.

Warnings of thunder and lightning mean that the launch rocket cannot be fuelled for safety reasons.

The launch was due tomorrow but has now been pushed back to Sunday afternoon, although weather forecasts for that time slot do not look good either.

"A lightning advisory early Thursday interrupted fuelling of the Delta II second stage rocket," said Nasa in a statement.

"Also, the temperature of the vehicle's second stage was too warm for the fuelling process to begin. However, the fairing temperature has been lowered so that another attempt can be made on July 6 pending acceptable weather."

Dawn will travel to two of the largest objects in the asteroid belt, Ceres and Vesta, and will send back vital information about the formation of the planets in the Solar System.

It is thought that the asteroid belt may be an accumulation of matter that could not reach critical mass to join together to form a planetary body.

Ceres is thought to be covered by a thick layer of ice up to 120km deep, with the possibility of liquid water underneath.

Vesta is a dry asteroid, but its diameter of 530km means that it accounts for around 10 per cent of the total mass of the Asteroid Belt.

If the probe launches successfully it will reach Vesta in late 2011 and go into orbit for seven months. It will then set of for Ceres, arriving in February 2015.