India expressed disappointment Friday with the 35-year sentence given to an American who admitted his role in the 2008 Mumbai attack, saying he deserved more prison time for the terrorism that killed 166 people in the country's financial capital.

David Headley was sentenced Thursday in a U.S. federal court in Chicago. External Affairs Minister Salman Khurshid said he would have possibly received a "more serious and severe" sentence had he been tried in India.

"The 35-year sentence is a beginning. We will continue our efforts to ensure that he is extradited and brought to India for trial," Khurshid told reporters.

Headley, 52, was born in the U.S. to a Pakistani father and an American mother and changed his birth name from Daood Gilani. He admitted that he helped plan the attack and videotaped targets that were later attacked.

In the three-day rampage, 10 gunmen from a Pakistani-based militant group fanned out across Mumbai, attacking a crowded train station, a landmark hotel and a Jewish center, among other targets.

Headley was arrested in the U.S. in 2009 and entered into a plea bargain with U.S. investigators under which he provided information about terror networks.

The U.S. State Department on Friday defended the handling of the case, saying that from Washington's perspective, it was a "very positive example" of U.S.-Indian counterterrorism collaboration.

The department ruled out Headley's extradition.

"He's been tried, convicted, and will serve in the United States," spokeswoman Victoria Nuland said.