Trump tells OPEC to lower oil prices
"We protect the countries of the Middle East, they would not be safe for very long without us, and yet they continue to push for higher and higher oil prices!" he tweeted.
"We will remember. The OPEC monopoly must get prices down now!"
Trump has earlier called for members of the Organization of the Petroleum Exporting Countries -- primarily cartel kingpin and U.S. ally Saudi Arabia -- to raise their production, and warned importers to stop buying oil from Iran or face U.S. sanctions.
Two of OPEC's founding members, Iran and Venezuela, are under sanctions from Washington.
A new set of U.S. sanctions is due to hit the Islamic republic's oil industry on Nov. 4.
Output from Iran has hit its lowest level since July 2016, according to the International Energy Agency, as top buyers India and China have distanced themselves from Tehran.
In 2016, major producers, both within and outside OPEC, agreed to slash production in an attempt to boost prices following the 2014 oil market crash.