Washington, Jan 26 (IANS) The United States virtually ruled out the extradition of Pakistani American David Headley to India even as New Delhi expressed disappointment at the 35-year sentence given to him by a Chicago court.

India wants Headley aka Daood Gilani, a key plotter of the 2008 Mumbai terror attack to be extradited to so he can face a 'harsher' sentence than he received in the US.

"The Justice Department spoke to this. He's been tried, convicted, and will serve in the United States," State Department spokesperson Victoria Nuland said Friday when asked about a report that India wanted to keep up the effort to extradite Headley.

Acting US Attorney Gary S. Shapiro, told reporters in Chicago Thursday that in order to extradite Headley to India, Headley would have to violate his guilty plea by not co-operating with the US government or any foreign government in future investigations and by not being truthful.

"Under the plea agreement, he cannot be extradited to India for the crimes he has been convicted of here. If the plea agreement was voided, then our agreement as to extradition is voided as well," he said.

Under the plea deal, US prosecutors "had agreed not to seek the death penalty against him and to not extradite him to Pakistan, India or Denmark for the offences to which he pleaded guilty."

Back in Washington, Nuland said: "From our perspective, justice was served, and this is a very positive example of US-Indian collaboration in the counterterrorism realm."

"The investigation and the prosecution of David Headley stems from the unprecedented and intense collaboration between the United States and Indian authorities in the counterterrorism sphere to bring all the people responsible for Mumbai to justice," she said.

Underscoring a statement by the Justice Department on the Headley trial, Nuland said "a key conspirator in the Mumbai terrorist attacks has been brought to justice in the United States."

"He will serve 35 years in prison for his role in these heinous acts that claimed the lives of 166 people, including six Americans," she said.

Headley, Nuland noted provided information of substantial value in US efforts against terrorism,.

This included testifying against co-conspirator Tahawwur Rana, providing extensive detail about accused terrorist Ilyas Kashmiri and his network, who was indicted in 2009 as well as submitting to questions from Indian law enforcement and working with US investigators.

Asked what message would it send from the Secretary of State Hillary Clinton, Nuland said: "That we promised that justice would be served, that justice is being served in this case."

(Arun Kumar can be contacted at arun.kumar@ians.in)