Claiming to have detected another Pakistani link into the audacious Mumbai attacks, investigators have said that payment for the Voice over Internet Protocol (VoIP) connection used by terrorists was made from port city of Karachi.

With the assistance of western investigating agencies including FBI and Scotland Yard, Indian investigators have found that the account was purchased on a fake identity card in Karachi and the payment of $300 (about Rs 15,000) was routed through a prominent money transfer service, official sources said.

An identity check carried out by the foreign investigators revealed that the documents used to get connection were fake, they added.

The VoIP number brought from Orlando, Florida [Images], was used by the 10 terrorists to talk to their masters across the border, including Zaki-ur-Rahman Lakhwi, the Lashkar-e-Tayiba operative believed to be the mastermind of the Mumbai terror strikes that left 183 dead.

Lakhwi is among 20 other LeT operatives detained by Pakistan government in a swoop couple of days back, the sources said.

VoIP is a technology that enables a person to make and receive phone calls through Internet. Voice is converted into packets of data sent over the Internet through a broadband connection, and reassembled at the other end of the line.

Investigators, who monitored worldwide traffic of VoIP found that nearly 5000 calls were made across the globe at the time of terror strikes in Mumbai. A critical analysis and decoding of data packets led them to two VoIP numbers, which were accessed from six Indian mobile phone numbers, the sources said.

Following fresh revelations the focus has now shifted to a Gulf-based satellite service operator, whose services were also used by the terrorists to connect with the LeT commanders in Pakistan.

The FBI team and Scotland Yard sleuths camping in Mumbai for last 10 days are interpreting all clues besides the Internet telephony signatures intercepted by Indian intelligence agencies.

The FBI team, which landed in India on December one, has been able to break the code of Internet telephony, its area of expertise.

As per the US laws, the FBI has to probe death or torture of any American citizen outside the US and later submit a chargesheet. Six US nationals were killed by terrorists in the Mumbai attacks.

The FBI has also sought interrogation report of Mohammad Ajmal Amir Iman, arrested by Mumbai police on November 26 from Chowpatty area.

The FBI is focusing on tracking back the mail as to what and how may times it was opened in Pakistan, the deciphered packets of the satellite conversation between the terrorists and their handler, and the air length frequency waves used for conversing on Internet.