Two United States Senators John Kyl, Republican from Illinois, and Richard Durbin, Democrat from Arizona, on Thursday wrote to Secretary of State Condoleezza Rice expressing concern over the growing relationship between India and Iran.

Citing media reports, the letter described the development as "troubling matters" in the context of 123 agreement with India. It quoted a report that said India recently sanctioned military-to-military working groups and joint training exercises with Iran.

The duo also cited several incidents of proliferation of dangerous technologies that had  its source in India. For example, it said, last year, two Indian companies were sanctioned for selling Iran precursor chemicals for rocket fuel and chemical weapons.

In 2004, the letter said, India was sanctioned by the US for nuclear proliferation violations when two former chairmen of India's Nuclear Power Corporation were identified as "allegedly passing nuclear secrets to Tehran".  The sanctions were dropped on one, while they remain in effect against the other, it said.

The Senators also brought into notice that "India apparently had helped Iran to develop more effective batteries for Iran's submarine fleet".

"This is particularly disturbing now that we have three United States Navy aircraft carrier battle groups on station in the Persian Gulf," the letter said.

The duo then went on to explain how India entered into agreements with Iran to develop oil and gas resources.

Mentioning that it understood India's reliance on external sources of natural gas, the Senators said the Iranian economy, its energy sector in particular, was extremely fragile.

They hoped India would not provide just the economic support to Iran that the United States had been labouring to deny through passage of legislation, including the Iran Sanctions Act.

Though the Senators said it supports the India-US civil nuclear deal, it was apprehensive that it could be "side-tracked' by the growing relationship between India and Iran.