The air force is concerned about the use of the ER-2 aircraft, the civilian version of the U2 spyplane, by Nasa for its atmospheric studies, because it is a single-seater and no-one can be aboard to monitor its missions, an air force source said.

The source said the Transport Ministry has instructed the air force chief and the air force to oversee the operations of all military aircraft in the kingdom.

To do this, the air force would have to put a specialist aboard the Nasa aircraft used in the climate studies proposed by the the US aeronautical and space agency.

"But the problem is the ER-2, an aircraft designed for spying missions, has only one seat, for the pilot. The air force would not be able to place anyone on board. Its flight ceiling is 60,000 feet, making it very difficult for its flight to be followed," the source said.

Therefore, the agreement to be made with the US should include the requirement that Nasa gives all details to the air force for examination, he said.

Air Marshal Monthon Satchukorn, the air force spokesman, said the air force was still waiting for a clear order from the government concerning Nasa's proposed use of U-tapao.

"The concern over the ER-2 aircraft is that it is still not clear to what extent it will be used and what the air force will have to watch for in particular. 

"We are waiting for information from agencies directly responsible for this matter, the Foreign Affairs and Science and Technology ministries," he said.

The spokesman said the air force was ready to comply with the government's order. If the order concerns flight plans, then aeronautical radio must also be involved, he added.

Adm Khanat Thongphoon, commander of the Royal Thai Fleet, said Nasa had not delivered any aircraft or research equipment to U-tapao.

Prime Minister Yingluck Shinawatra had ordered the navy to clarify the matter.

Adm Khanat said U-tapao airbase had been used in May for the delivery of US military equipment for two exercises - Cobra Gold and CARAT 2012. After the completion of the exercises all aircraft and equipment had been moved out.

He said Nasa's request for use of U-tapao was still being considered by the government and the navy had not made any special preparations for it. He expected the matter would be considered by the cabinet on Tuesday.