GENEVA (Reuters) -- China has conditionally given a Swiss-British duo permission to fly over its territory in their round-the-world balloon attempt, a spokesman for the mission said on Saturday.

Gerard Sermier, spokesman for the Breitling Orbiter 3 mission, said the conditions were stringent and would make it difficult for meteorologists to plan an authorized trajectory.Swiss psychiatrist Bertrand Piccard and British co-pilot Brian Jones could take off from the Swiss Alpine village of Chateau-d'Oex on Thursday at the earliest, he said.

China banned balloons from flying over its territory after British tycoon Richard Branson and American Steve Fossett drifted into a banned zone of its airspace during their circumnavigation attempt in December and did not land when ordered to do so.

"We have received the written approval from the Chinese authorities which confirms the terms which Bertrand agreed to last Thursday at the Chinese embassy in Berne. The conditions are very strict," Sermier said.

"China will allow us to fly north of the 43rd parallel, in other words over Mongolia, or south of the 26th parallel, the Himalayas. The latter option is the only feasible one."

Piccard, 40, is making his third attempt to circumnavigate the globe, one of the last remaining aeronautical challenges. Jones, 52, spent 13 years in the Royal Air Force.