India's two biggest importers of crude oil from Iran will cut shipments from the Islamic republic by at least 15 percent this financial year due to US pressure, a report has said.

Washington has been seeking to shut down Iran's oil trade to put pressure on the Persian Gulf nation to abandon its disputed nuclear programme.

The Indian government has asked state-owned Mangalore Refinery & Petrochemicals and privately run Essar Oil to lower their imports in the current financial year, Dow Jones News Wires said late Wednesday.

The reported step comes ahead of a trip to India early next week by US Secretary of State Hillary Clinton, during which India's purchases of Iranian oil are expected to be discussed.

The news agency cited in its report two unnamed people who it said had direct knowledge of the Indian government request that was made as a result of US pressure.

A spokesman for India's government was not immediately available for comment but New Delhi has been reported by domestic media to be seeking to diversify its oil purchases.

India and the United States are navigating some of the choppiest waters since they began to build closer ties in the late 1990s with Washington pushing New Delhi to significantly cuts oil imports from Iran.

Dow Jones said Clinton had told U.S. Congress earlier in the year that India was helping in putting pressure on Tehran much more than New Delhi's public statements on the issue showed.

India imports four-fifths of its crude oil to feed its growing economy and has said it needs to keep buying Iranian oil to supply its requirements.

The country has struck a deal with Iran to pay for around half of its oil imports from Tehran in Indian rupees as a way to bypass banking sanctions that have made it virtually impossible to pay for the purchases in US currency.

Iran has repeatedly rejected charges by Western nations that it is developing an atomic bomb but the United States and the European Union have imposed stiff sanctions to persuade Tehran to shelve its nuclear programme.