Indian prime minister Manmohan Singh voiced "serious concerns" to David Cameron over corruption allegations relating to the sale of Westland helicopters to his country's air force, as the two men met for talks in New Delhi.
Mr Singh's decision to raise the issue in a joint press conference with Mr Cameron cast a shadow over a trade mission designed by the British premier to promote a "special partnership" between the UK and India.
Mr Cameron promised to provide any information requested by the Indian authorities, but stressed that the case was for Italian investigators to probe, as AgustaWestland is owned by Italian firm Finmeccanica.
India suspended payments under the £480 million contract following the arrest last week of Finmeccanica chairman and chief executive Giuseppe Orsi and AgustaWestland chief executive Bruno Spagnolini on corruption and tax fraud charges.
Sitting alongside Mr Cameron following their talks at Hyderabad House, Mr Singh said: "I... conveyed to the Prime Minister our very serious concerns regarding allegations about unethical means used in securing the 2010 contract for AgustaWestland helicopters.
"I told him that we have sought an explanation from the company by February 22 to examine if the contractual conditions on unethical practices and the integrity pact have been violated.
"I have sought full assistance from the UK in this case. Prime Minister David Cameron has assured me of the co-operation of his Government in the investigation."
Mr Cameron said: "In terms of AgustaWestland, we will respond to any request for information. I am glad that the Italian authorities are looking into this issue in detail, as Finmeccanica is an Italian company."