New Delhi, May 12 (IANS): The Central Bureau of Investigation (CBI) Thursday questioned Prashant Ruia, the chief executive officer of the Essar group, for irregularities in the allocation of 2G spectrum airwaves, an official said. Officials of the Khaitan Group have been summoned in the same case.

"Prashant Ruia was questioned Thursday in 2G spectrum case. He arrived at 10.30 a.m. at the CBI headquarters here and was quizzed till 1.30 p.m." CBI spokesperson Dharini Mishra told IANS.

A CBI official said Ruia was questioned in connection with violation of a rule that bars one entity from holding more than 10 percent stake in two or more mobile operators in a service area.

"He was asked about the conglomerate's ownership in Loop Telecom Pvt. Ltd. when it got licences in 2008," said the official, adding that the Essar group already had a 33-percent stake in another telecom entity. Ruia was previously questioned in February.

The official said the agency also called Khaitan Group members to enquire about their alleged ownership in Loop Telecom.

He said the Khaitan group chief has family ties with Essar group. The names of Khaitan officials summoned by the CBI were not revealed.

Mishra said that Ruia could be called again after a joint team of the Enforcement Directorate and the CBI returns from Mauritius, where it has gone to investigate the money trail of the scam.

"Another joint team will be going to Mauritius this week in this case," Mishra said.

The CBI had earlier told the Supreme Court that Kiran Khaitan has a holding in Loop Telecom and she is the sister of Shashi and Ravi Ruia, who are the chairman and vice chairman of the Essar group, respectively.