India's imports of Iranian crude oil rose last month to their highest level since March 2014 as refiners boosted purchases ahead of a final push by the international negotiators to reach a deal on Tehran's nuclear program by end-June.

The jump to a 14-month high comes just two months after India dropped its crude imports from Iran to zero under US pressure to limit its purchases of the Islamic republic's oil, Reuters reported.

India, the world's fourth biggest oil consumer and Tehran's top client after China, shipped in 367,900 barrels per day (bpd) of Iranian crude in May in nine vessels, up 39 percent over April, according to preliminary data from trade sources and a report compiled by Thomson Reuters Oil Research and Forecasts.

The May imports surged by two-thirds from a year ago, the data also showed.

Mangalore Refinery and Petrochemical Ltd was Iran's biggest Indian client in May shipping in about 207,400 bpd from Iran, the data showed.