The Delhi Police arrested another petroleum ministry employee in connection with the alleged theft of official documents for the purpose of sale to consultants and private companies.
The crime branch of the Delhi Police also registered another FIR and planned to visit offices of the ministry to investigate the case, a television channel reported.
Monday's arrest was the third of a ministry employee.
The police interrogated five corporate executives arrested in the case at the crime branch office on Sunday.
Sources said two top officials of a major oil firm were summoned to join the investigation but while one was down with swine flu, the other was out of the country.
On Monday, the Anil Ambani-led Reliance group distanced itself from reports of police raids at its offices, saying it was "not aware of the circumstances" leading to the arrest of an employee of the group's power business.
"No search or raid has been conducted by police authorities at any office of the Reliance Group anywhere in India," the group, which has interests ranging from telecom to power and infrastructure, said in a statement.