Iran's crude oil exports fell for the first time in five months in March, and are slated to drop further in April, moving closer to the levels stipulated by November's temporary nuclear deal that eased some sanctions on Tehran.
Under the agreement reached in Geneva, Iran's oil exports were to remain at an average 1 million barrels per day (bpd) for the six months to July 20, but since the signing last year, shipments to Asia alone had topped that mark until this month.
The drop in crude exports to just over 1 million bpd in March and to 953,000 bpd for April, according to ship loading data seen by Reuters, reduces pressure on Tehran ahead of talks next month to finalize an end to the decade-old nuclear dispute.
The drops have come mainly because Japan did not take any cargoes in March and South Korea is not scheduled to take any shipments in April, according to the tanker data.
"When the Iranian exports increased, the market noticed so I'm not surprised that they might try to cut back some in the upcoming period," IHS oil consultant Victor Shum said.
"As far as China is concerned, the offtake is a bit higher, but it goes up and down, so on average, for the year, China will keep it under the target," he said.
Iran's biggest customer China will increase loadings this month to 552,000 bpd, about a third higher than a year ago, after a decline in March to 458,000 bpd.
Chinese buyers will account for almost 60 percent of oil shipped by tanker from Iran in April.
Crude going to India, Tehran's No.2 customer, surged nearly 43 percent in the first quarter of 2014, bringing a warning from the United States that it needed to hold the shipments closer to end-2013 levels of 195,000 bpd.
India is scheduled to load in April about 145,000 bpd of Iranian crude, down from imports of 412,000 bpd in January.
It's not immediately clear if the reductions in Japan, India and South Korea are a response to pressure to hold to the terms of the temporary nuclear agreement, or if they are related to a seasonal drop in imports because of refinery maintenance.
Tehran denies that its atomic energy program is a front for developing nuclear weapons, and says it seeks only electricity from its enrichment of uranium.
In the second half of the last decade Iran was pumping around 4 million bpd, but tough international sanctions the past two years have slashed the country's oil production and exports.
The temporary deal between Iran and world powers, struck in November and implemented on Jan. 20, also freed up $4.2 billion in back oil payments to Tehran in return for curbs on its nuclear program.
Negotiators from Iran and the United States, Russia, China, Britain, France and Germany, known as P5-plus-one, will begin their next round of talks in the Austrian capital on May 13.
Seasonal maintenance plans may explain why Japan and South Korea area are loading less oil from Iran, Shum said.
"Q1 may be still part of the winter season and there is a bit of a peak in demand, but in Q2 typically the crude demand starts to come down with the spring maintenance," he said.
Buyers from Japan may also have held off from loadings amid uncertainty over whether Tokyo would roll over a sovereign insurance scheme to cover oil shipments after commercial insurers complied with an EU ban on coverage for Iranian oil.
Iran's oil exports, including condensate, totaled 1.25 million bpd in March, down 19 percent from 1.55 million bpd in February. They are set to fall almost 5 percent further in April to 1.19 million bpd, according to the loading data.
Earlier this month, the International Energy Agency had pegged Iran's crude shipments in February at 1.65 million bpd - including condensate - the highest since June 2012.
Iran's deputy oil minister for international trade said on Monday that the Islamic republic's oil exports had held at around 1 million bpd for the last six months.
South Korea loaded 129,000 bpd last month compared with 217,000 bpd in February and will load no crude during April, according to the tanker data obtained by Reuters.
Japan, the other of Iran's four biggest buyers, didn't load crude in March, but Japanese tankers are scheduled to pick up 146,000 bpd this month, compared with 119,000 bpd in February.
Turkey is the other main destination for loadings in March and April. Since sanctions were imposed in 2012, more than halving Iran's oil sales, China, India, South Korea, Japan and Turkey have bought nearly all of Tehran's crude exports.