The move by Indian security agencies will have to be ratified by the government, but shows every sign of being passed, as it comes after unconfirmed reports that terrorists were using internet telephony links in the Mumbai attacks.

According to the Reuters newswire, the Indian security agencies are concerned that militant groups from outside of Indian are using internet telephony to bypass telephone monitoring systems used by security agencies around the world.

Until a few years ago, terrorist groups made extensive use of satellite telephony for their critical calls, as the call routing on some systems was from one satphone to another via a single satellite, with no downlink.

That loophole has been quietly closed by the satellite telephone carriers, Infosecurity notes, as all calls are now downlinked to the nearest earthstation before being routed back out to the satellite telephone network.

Ironically, this is not due to security concerned, but due to the introduction of packet-based switching, which underlies most telecommunications systems, whatever the network topology,

Reuters quotes an anonymous Indian intelligence bureau official as saying that, "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."

Indian telecommunications secretary Siddharth Behura has reportedly confirmed that requests had been made to providers to "block some calls", but no further details have been revealed to the media.

According to Reuters, India launched a security review of its communications monitoring systems after Islamist militants killed 166 people in Mumbai in November of last year.

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