WASHINGTON (WASHINGTON POST) - President Donald Trump on Thursday (Sept 20) again urged Middle East oil producers to unleash their giant petroleum reserves and drive down the price of oil.

But this time he added a new threat by drawing the US-Mideast military umbrella into the equation.

"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! We will remember. The Opec monopoly must get prices down now!" Trump tweeted.

The United States maintains a large military presence in the region, including naval forces that keep the sea lanes open for oil tankers. The United States relies on those tankers for its oil imports.

Crude oil prices have been rising over the past year as a result of the Organisation of the Petroleum Exporting Countries' strategy to tighten supply. Prices hit a two-month high Wednesday as Brent crude - the world's most closely followed gauge - rose above US$79 a barrel.

This has helped lead to higher prices at the pump. Gas prices have risen to their highest levels in four years and were about US$2.85 a gallon over the Labour Day weekend.

Gas prices are reducing Americans' spendable cash as voters head to the polls for the midterm elections in November.

The President has tweeted several times that he wants low oil prices, prodding Opec to simply open its spigots.

At the same time, Trump will reimpose sanctions on Iran later this year as part of his decision to withdraw from the nuclear deal, potentially removing a significant oil supplier from the market.