NEW DELHI, July 11 (Reuters) -

India's oil imports from Iran declined by 15.9 percent in June, the first month after the United States said it would reimpose sanctions on the country, according to data from shipping and industry sources.

In June, India imported 592,800 barrels per day (bpd) of oil from Iran compared to 705,200 bpd in May, the data showed. The sources declined to be identified.

India, Iran's top oil client after China, has asked refiners to look for alternative oil supplies as the nation may have to drastically cut imports from Tehran to comply with the renewed U.S. sanctions.

The United States in May said it would reimpose the sanctions after withdrawing from a 2015 agreement with Iran, Russia, China, France, Germany, and Britain, where Tehran agreed to curb its nuclear activities in return for the lifting of earlier sanctions.

Lower purchases by private refiners dragged down India's June imports from Iran although state refiners stepped up purchases.

State refiners, accounting for about 60 percent of India's nearly 5 million bpd of refining capacity, lifted about 10 percent more Iranian volumes in June compared to May, at about 454,000 bpd, the data showed.

Indian state refiners had cut oil imports from Iran in the 2017/18 financial year because of a dispute over the development rights for an Iranian natural gas field.

However, the state refiners had drawn plans to raise imports in the current fiscal year starting in April after Iran offered free shipping and an extended credit period of 60 days.

In April to June 2018, the first quarter of this fiscal year, India's oil imports from Iran rose by about 24 percent to about 647,000 bpd from the previous quarter, the data showed.

Imports by state refiners during the period more than doubled to about 413,400 bpd from 191,700 bpd, the data showed.