With India unwilling to accept dictation from external powers, relations between India and Iran may cause policy differences between New Delhi and Washington, says a new Congressional study.
This, however, is unlikely to derail their own "global partnership", the study adds.
While US policy is to isolate Iran and to ensure that its nuclear programme is used for purely civilian purposes, India has never shared US assessments of Iran as an aggressive regional power, notes the Congressional Research Service report.
As US relations with India have grown both deeper and more expansive in the new century, some in Washington believe that New Delhi's friendship with Tehran could become a significant obstacle to further development of Indo-US ties.
However, India-Iran relations are unlikely to derail the further development of the Indo-US global partnership, the report on "India-Iran Relations and US Interests" by K Alan Kronstadt and Kenneth Katzman said.
At the same time, given a clear Indian interest in maintaining positive ties with Iran, especially in the area of energy commerce, New Delhi is unlikely to abandon its relationship with Tehran or to accept dictation on the topic from external powers, it opined.
Similarly, Iranian leaders, always looking for new allies to thwart US attempts to isolate Iran, echo the positive sentiments and say that India's current relations with the US will not weaken their own ties with New Delhi.
Many in US Congress voice concern about India's relations with Iran and their relevance to US interests. Some worry that New Delhi's policies toward Tehran's controversial nuclear programme may not be compatible with those of Washington, the report said.
There are further US concerns that India plans to seek energy resources from Iran, thus benefiting financially a country the US seeks to isolate.
Indian firms have in recent years taken long-term contracts for purchase of Iranian gas and oil, and India supports proposed construction of a pipeline to deliver Iranian natural gas to India through Pakistan.
The Bush administration has also expressed strong opposition to any gas pipeline projects involving Iran, but top Indian officials insist the project is in India's national interest.
Positive and potentially deepening India-Iran relations present a challenge to US policymakers, the Congressional report said, taking note of "signs" that in the wake of their July 2005 accord, India is bringing its Iran policy into closer alignment with that of the US.
There is in India a sizeable constituency urging resistance to any US pressure that might inhibit New Delhi-Tehran relations and decrying any Indian policies, which prioritise relations with the US in disregard of India's national interests, it said.
While top Indian leaders state that friendly New Delhi-Tehran ties will continue concurrent with - or even despite - a growing Indo-US partnership, some observers see such rhetoric as incompatible with developments over the past year.
The Indian government has made clear that it does not wish to see a new nuclear weapons power in the region and, in this context, it has aligned itself with international efforts to bring Iran's controversial nuclear programme into conformity with Non-Proliferation Treaty and IAEA provisions.