"Our expectation is for OPEC+ output to increase in the second half of 2019 as members chase higher oil prices but ultimately will contribute to an oversupplied market", said Edward Bell of Emirates NBD bank.
Worldwide benchmark Brent crude was trading at $71.19 per barrel at 0615 GMT for a 1.33% decline after it closed Friday at $72.15 a barrel.
Stephen Innes, head of trading at SPI Asset Management, said the producer group "will want to avoid at all cost oil prices surging to levels that will trigger demand devastation, (while) it is clearly in Opec's best interest to maintain a solid floor on prices".
USA sanctions against Iran have denied its government more than $10 billion in oil revenue, a US official said earlier this month.
Traders said the market was shifting its focus to the voluntary supply cuts led by OPEC, de facto headed by the world's top exporter Saudi Arabia.
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Sweden's SEB says Beijing could lift its imports of Iranian crude in the coming months from some 600,000 barrels per day in March to around 1 million bpd, bucking US pressure, while exports elsewhere under the sanctions radar could reach another 500,000 bpd.
OPEC and Russia-led non-OPEC agreed on December 7, 2018 to cut their total output by 1.2 million barrels per day in order to bring balance to the global oil market and raise crude prices.
Analysts and market participants have downplayed the comments since details were unclear. Earlier this year Iran's President Hassan Rouhani said the country faced its biggest economic challenge since the Islamic revolution of 1979.
However, Brent reversed its downward course after Oman energy minister Mohammed bin Hamad al-Rumhy said that the Organization of the Petroleum Exporting Countries (OPEC) was intending to extend supply cuts at its June meeting. The U.S. withdrawal of waivers on Iranian oil exports is likely to further impact this figure.
"Over the past week we have seen heavy, sweet crude differentials rising markedly, as the long-awaited IMO impact has started to leave its mark on the crude market", JBC Energy said in a note on Monday.
Belarus said on Tuesday that months of work would be needed to restore clean oil supplies via the Druzhba pipeline from Russian Federation to Europe after Western oil consumers suspended imports of Urals crude due to contamination.