Thiruvananthapuram, Nov 25 (IANS): A CBI team raided the office of the Airport Authority of India here on Tuesday, a source said on Wednesday.

The raid was kept a closely-guarded secret and the details came to light only on Wednesday.

The Thiruvananthapuram unit of the CBI has been closely monitoring the situation for the past six months after allegations of royalty evasion that the ground handling agencies pay to the Airport Authority of India had cropped up.

A person in the know of things told IANS that the day-long raid ended after the CBI officials took away with them documents related to the ground handling charges.

George Tharakan, the AAI official in charge here, was not forthcoming when IANS got in touch with him to know the details of the probe.

"I don't know," said Tharakan and disconnected the call. 

The CBI had a few months back met all the international airlines besides national carrier Air India and got a detailed statement of the ground handling charges that they have paid to the ground handling agencies since 2012.

At present there are two ground handling agencies, including a joint venture of the national carrier, that operate at the international airport here.