A group of influential lawmakers in the US have sent a letter to Prime Minister Manmohan Singh warning that India's 'strengthening relationship' with Iran will be a factor when Congress finally votes on the civilian nuclear deal.

The warning came despite assertion by visiting Foreign Secretary Shivshankar Menon on Tuesday that India's dealings with Iran were not in any way a contravention of the UN Security Council resolutions.

The letter to the prime minister has listed, what the lawmakers say, a series of recent meetings between Indian and Iranian officials as indications of growing cooperation between the two countries on military and energy issues.

'We must stress that the subject of India's strengthening relationship with Iran will inevitably be a factor when Congress votes on the final language of the nuclear agreement', the letter said, according to a report in The Washington Post.

Lawmakers 'are not just alarmed but actually outraged by India's outreach to Iran', an unnamed aide was quoted as saying in The Post.

The letter has been signed by Tom Lantos, Chairman of the House Foreign Affairs Committee; Ileana Ros-Lehtinen, the ranking Republican; Howard Berman, Gary Ackerman who is the Chair of the House Middle East and South Asia subcommittee; Mike Pence, the subcommittee's ranking Republican; Brad Sherman, Chairman of House subcommittee on terrorism and non-proliferation and Ed Royce that subcommittee's ranking Republican.

'It is difficult for us to fathom why India, a democracy engaged in its own struggle against terrorism, would want to enhance security cooperation with a repressive government widely regarded as the world's most active state sponsor of terrorism', the letter said.

It added that 'India's pursuit of closer relations with Iran appears to be inconsistent with the letter and spirit' of President George W Bush and Dr Singh's announcement of a 'global partnership' between the two countries.

Congressional aides, according to the report, have said that a subtext of the letter is growing concern in Congress that the administration is too eager to wrap up negotiations with India.

On Tuesday evening after finishing two days of hectic talks with senior functionaries of the Bush administration Menon was asked at a press interaction on Congressional concerns on Iran.

Menon for his part argued that he was not sure where these stories of India's deepening military engagement with Iran are coming from but firmly maintained that New Delhi's ties with Tehran are not in violation of any United Nations Security Council resolutions.

"Nothing that India does with Iran is in any way contravention of the United Nations Security Council resolutions. Much of what we do is normal between states and done with Iran by several other states," Menon said.