India's security agencies have recommended a ban on international Internet telephony until a system to trace the calls is in place, officials said, the latest move to plug security loopholes after the Mumbai attacks.

India fears that militant groups operating from overseas could use Internet telephony to bypass security systems during the planning and execution of attacks, officials said.

"Since it is impossible to trace Internet telephone calls from foreign countries, we have asked the Department of Telecommunications to block such calls until a system is in place," said a senior Intelligence Bureau official, who could not be identified.

Indian Telecommunications Secretary Siddharth Behura confirmed that requests had been made to providers to "block some calls", but revealed no further details.

Several providers, including Skype, Google, Yahoo and Windows Live offer Voice Over Internet Protocol (VOIP). Any ban would affect thousands who use the Internet to make cheap phone calls within and outside India.

Many companies in the Gulf offer this service to India and if a ban is imposed, such companies and their customers will be severly hit, said a telecom expert.

India has launched an overhaul of its security systems after Islamist militants killed 166 people in Mumbai in November 2008.

Police recovered a satellite phone and said the militants had kept in touch with their handlers in Pakistan on mobile phones and Internet telephony.

"There have been so many instances when shooters arrested by us said they have got instructions from abroad through Internet systems," said Rakesh Maria, a senior police officer in Mumbai.

Last year, India said it was concerned about e-mails sent through Blackberry services that could not be traced or intercepted. The company later agreed to comply with India's security directives after a series of meetings.

India is also considering a new law allowing for checking of all imported telecommunications equipment to ensure it does not compromise national security.

In the January-March period this year, 130 million minutes of Internet telephone calls were made in India, according to the Telecom Regulatory Authority of India.

The Internet Service Providers Association of India (ISPAI) said it would comply with all security requirements. "We still don't think the security agencies are against Internet Telephony. Rather, they want it to work under a proper mechanism," said Naresh Ajwani, Secretary of ISPAI. - Reuters