Iran had been pushing hard for oil producers to hold output steady as US sanctions are expected to hit its exports.
"We will surely do something to thwart the U.S. rallying cry that Iranian oil (exports) must be stemmed", First Vice President Eshagh Jahangiri said in statements broadcast on state television.
But Saudi Arabia, OPEC's biggest producer, was keen to raise output to meet calls from U.S President Donald Trump and major consumers such as India and China to help cool oil prices and avoid shortages, according to Saudi officials including Energy Minister Khalid al-Falih.
National Basketball Association superstar LeBron James signs with LA Lakers
Because they own his "Bird rights" the Cavs can offer James more money than any other team - a five-year, $207 million deal. Many in the Los Angeles sports community were quick to cheer the move and welcome the newest Lakers legend.
OPEC and non-OPEC countries said they would raise supply by returning to 100 percent compliance with previously agreed output cuts, after months of underproduction.
In Sunday's letter, Iranian Oil Minister Bijan Zanganeh didn't mention Saudi Arabia by name, but urged members to adhere to the bloc's agreement last month to pump an additional one million barrels of crude oil a day in July.
"Our attempt is to defeat USA policies in the sale of oil and we are pretty sure we will sell our oil as much as we need", he said.
"They're begging the Saudis to raise their output so that if Iran's quota decreases nothing will happen to the markets", said Jahangiri.
At least 40 killed in bus accident in northern India
After the incident, Police and National Disaster Management Response Force (NDRF) rushed to the spot to rescue people. The 28-seater bus was carrying 59 passengers, police said, adding a probe will determine the reason of the accident.
The deal allowed Iran to sell its crude oil again on the global market, a major cash infusion for its anemic economy, long hobbled by worldwide sanctions.
"We're not granting waivers", the official said. "We believe that the Russian budget received an extra 4 trillion rubles thanks to this deal with Saudi Arabia", said the head of RDIF Kirill Dmitriev in an interview with Russia's NTV channel.
"In this battle", he said, "any country that tries to take Iran's place on the oil market will be guilty of treason against Iran. and surely one day it will pay the price of this treason".
Iran and Saudi Arabia broke off diplomatic relations in 2016 and are locked in several proxy wars in the Middle East, including in Yemen. The letter, published by the Iranian Oil Ministry's SHANA news agency, did not directly name Saudi Arabia, Iran's Mideast rival, but the ultraconservative kingdom was clearly its target.
Lakers will meet with Clint Capela
The Rockets can sign Paul to a max contract worth $205 million over five seasons, and they can match any offer made to Capela. Last season, the Rockets were the No. 1 seed in the Western Conference, and they finished with the NBA's best record at 65-17.