India on Wednesday called a declaration that Pakistan's intelligence service and former chiefs enjoy immunity in a case related to the 2008 Mumbai attacks a "serious disappointment".
The Indian government has long asserted that Pakistan's powerful Inter-Services Intelligence agency was behind the Islamist attacks which left 166 people dead -- an accusation denied by Islamabad.
The Indian statement was in response to an affidavit filed in a US court earlier in the week in which the US government said Pakistan's ISI and its former chiefs, Ahmed Shuja Pasha and Nadeem Taj, "enjoy immunity" in the Mumbai attacks.
The US affidavit is "a matter of deep and abiding concern", the Indian government statement said, noting Washington has publicly said it is committed to bringing "those responsible for the Mumbai terror attacks to justice".
"The decision of the US authorities in this case is a cause of serious disappointment," said the Indian statement.
The New York federal court is hearing a case filed by US survivors of the Mumbai attacks and family members of the victims against Pasha, Taj and other ISI officials.
Leaders of Lashkar-e-Taiba (LeT) militant group, including its founder Mohammed Hafiz Saeed, are also named in the suit. India has accused Pakistan's ISI of collaborating with the LeT to mount the attacks.
The US government insisted in its affidavit that Pakistan must take steps to dismantle the LeT and support India's efforts to counter militant threats, according to the Press Trust of India (PTI).
But at the same time the affidavit said, "the ISI is entitled to immunity because it is part of a foreign state", the PTI report stated.
India last month hanged Pakistani national Mohammed Ajmal Kasab, the lone surviving gunman of 10 attackers who raided targets including top hotels and a Mumbai railway station while holding elite Indian special forces at bay.