Sanctions-hit Iran on Saturday blasted fellow OPEC members Saudi Arabia, Kuwait and the United Arab Emirates as oil quota "violators", accusing them of depressing global crude prices by over-pumping.
Iran's OPEC representative, Mohammad Ali Khatibi, said Tehran had officially protested to the cartel that Saudi Arabia was "saturating the market" under pressure from the United States and the European Union, according to the official IRNA news agency.
"It is not right that two or three countries compensate for a country that is being sanctioned. OPEC members should not work against each other," Khatibi was quoted as saying.
Iran is the second-biggest producer in the Organisation of the Petroleum Exporting Countries after Saudi Arabia.
It has repeatedly lashed out at Saudi Arabia, a US ally, for opening oil spigots to make up for a shortfall in the market resulting from a cut in Iranian crude sales because of Western sanctions.
In the first quarter, Saudi output swelled by 250,000 barrels per day to 9.9 million bpd from a year earlier, according to OPEC estimates.
At the same time, OPEC said Iranian production dropped by 300,000 bpd to 3.2 million bpd, its lowest level in 20 years. Iran disputes that, saying its output has increased to 3.8 million bpd.
"Saudi Arabia, and two of its allies are the biggest OPEC (quota) violators," Khatibi was quoted as saying, referring to Kuwait and the United Arab Emirates.
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He called that "the main reason for a drop in oil prices in the market."
Saudi Arabia, he said, "is under pressure" from the United States and Europe to pump more ahead of a July 1 EU oil embargo on Iranian crude exports.
The Iran-Saudi row was likely to colour the next meeting of OPEC, to take place Thursday in Vienna, with Tehran expected to push for OPEC members to stick to their agreed quota levels.
Global oil prices this year spiked high on fears of a US or Israeli military confrontation with Iran over the Islamic republic's disputed nuclear programme.
Prices fell back markedly when Iran agreed to hold talks with the so-called P5+1 -- Britain, China, France, Russia and the United States, plus Germany -- but have inched back up as it becomes clear that those talks are faltering.
On Friday, Brent North Sea crude for July delivery was at $99.47 a barrel in London trade, close to the $100 target aimed for by Saudi Arabia and Kuwait.
Iran is more hawkish on prices, keen to earn more per barrel to offset the forced lowering of demand for its oil.
"Iran and some other OPEC members, such as Venezuela and Algeria, are against" an increase in quotas, Khatibi said.
In the OPEC meeting, Iran is also expected to push the nomination of a former oil minister, Gholam Hossein Nozari, for the top post of OPEC secretary general.