India is the world's fourth-biggest oil consumer, importing four-fifths of its needs as its own output shrinks.
The United States wants India to wait for a final nuclear deal between Tehran and world powers before actively engaging with Tehran.
Oil prices dipped on Wednesday as the market prepared for a gradual increase of Iranian exports into an already oversupplied market from 2016.
ONGC is raising debt for a spate of acquisitions over the past year
There was a sharp fall in power output on Thursday from a plant in Gujarat that left India more than 9,000 megawatts short of peak demand, according to two officials at the state grid operator.
Investor confidence has evaporated amid fears over the rising cost of funding India's gaping current account deficit, prompting New Delhi to delay plans to raise much-needed funds through partial privatisations, finance ministry sources said.