India will seek extradition of US terror suspect David Headley from America after a chargesheet is filed against him in a court for his involvement in last year's Mumbai attack.

Union Home Secretary G K Pillai said investigation with regard to Headley, who had allegedly conducted recce and made videos of 26/11 targets before passing them to the Lashkar-e-Toiba attackers, was being done by the National Investigation Agency (NIA).

"When our investigation is complete, we will file a chargesheet in an Indian court. After filing the chargesheet, we will take a warrant of arrest. After getting the warrant of arrest, we will approach America (for extradition)," he told reporters here on way to Darjeeling on Sunday.

Headley, a 49-year-old American-Pakistani, has been in custody in the US since October three for plotting terror attacks. His accomplice Canadian-Pakistani Tahawwur Rana was subsequently arrested by the FBI.

Pillai is in Darjeeling to participate the tripartite talks among the Centre, West Bengal government and the Gorkha Janmukti Morch on the Gorkhaland issue.