The United States has said it has not seen the letter written by a group of American lawmakers to Prime Minister Manmohan Singh on New Delhi's ties with Tehran and its implications to the civilian nuclear deal but noted that the Bush administration has already raised the matter with the Indian government.

"We have not seen this letter and I am not sure whether the Indians have had a chance to look at it and react to it.

"In terms of what we say and while what we have discussed with our Indian counterparts, I know that we have raised Congressional concern about their cooperation with Iran and we continue to encourage the Indians to use what influence they have with the Iranians to press them to comply with UN Security Council resolutions and to behave responsibly in a wide variety of areas," Deputy Spokesman Tom Casey told media persons in reply to a query.

He said when Foreign Secretary Shivshankar Menon was in town meeting senior officials like the Under Secretary of State for Political Affairs Nicholas Burns and others he has had some 'fairly strong' views on the subject.

"But certainly this is an issue that we continue to discuss with them in our official contacts as well," he added.

Click to read the lawmakers' letter to Dr Singh

The strong-worded letter from Capitol Hill came from senior law makers like Tom Lantos, chairman of the House Foreign Affairs Committee, ranking Republican Ileana Ros-Lehtinen, Howard Berman, Gary Ackerman, who is the Chair of the House Middle East and South Asia subcommittee, and others.

"Regarding Iran, we are deeply concerned by India's increasing co-operation with that country, including the exchange of visits between high-level officials, enhanced military ties, and negotiations of agreements to establish closer economic relations," they said in the letter going on to list the kind of interactions New Delhi has had with Tehran.

"In March, the commander of the Iranian navy, Rear Admiral Sajjad Koucheki-Badelani, visited India at the invitation of Admiral Sureesh Mehta, the chief of the staff of the Indian Navy, to discuss the strengthening of military relations.

"A joint defense working group reportedly has been established and will meet later this year in Tehran to pursue broader co-operation in defense, including training Iranian military personnel," the senior law makers pointed out in their letter.

"Such co-operation raises renewed questions about the possible diversion of sensitive technology to Iran, for which Indian entities have been sanctioned in recent years, including US-origin technology provided to India in the context of civilian nuclear and space co-operation," they said.

"We are also concerned that broadened economic relations between India and Iran are being pursued. Among the most prominent developments is the agreement reached earlier this year for the construction of a major natural gas pipeline from Iran to Pakistan and India that will provide the government of Iran with billions of dollars of revenue," the lawmakers said.

"As strong proponents of closer ties between the United States and India, we are deeply concerned that the developments outlined in this letter have a significant potential to negatively affect relationship between the US and India in general and consideration by Congress of the 123 Agreement in particular," they said.

"Mr Prime Minister, we urge you to provide assurances that India will cease illicit procurement activities in the US, sever military cooperation with Iran and terminate India's participation in the development of Iran's energy sector. By taking these important steps, you can ensure that the positive evolution of our bilateral relationship continues," the lawmakers said.

Foreign Secretary Shiv Shankar Menon had expressed puzzlement as to the origin of the stories on the so-called India-Iran military engagement and argued that what

New Delhi did with Teheran was no different from what other countries did.