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 as the nation may have to drastically cut imports from Tehran to comply with the renewed US sanctions.

The United States said it would reimpose the sanctions after withdrawing from a 2015 agreement with Iran, Russia, China and several Western European countries where Iran agreed to curtail its nuclear activities in return for the lifting of earlier sanctions.