US President Donald Trump has said he does not think the Iran war will end until after November's midterm elections, adding that oil prices will not come down until then.

"I think the war's going to end immediately after the election because they can't hold out any longer," Trump said of Tehran on Wednesday.

His comments come as he heads to Texas for the party's first convention ahead of the midterms, when the balance of power in the US government could change.

Trump is facing falling polling numbers and pressure from within his Republican Party to end the war with Iran.

On Wednesday, oil prices rose to $100 (£74) for the first time since July, driven by heightened fighting in the Middle East.

"Right after the election, oil prices are going to be tumbling downward," Trump told reporters. "I think it's going to take a little bit longer than the midterm."

He added that Iran was "desperate to try and affect the election, so that we can get a nice weak group of people in there" - an apparent reference to the Democrats - "and leave them alone and let them have their nuclear weapon".

Tehran has repeatedly denied it is seeking nuclear weapons.

Trump also said further negotiations with Iran could possibly happen, "but it's not something we're looking at".

The US president initially predicted the war, which is now in its seventh month, would last only a matter of weeks. The conflict, and its knock-on effects on everything from gas to groceries, has led to a steep decline in his approval ratings.

Fighting in the Middle East has intensified in recent days, as oil facilities throughout the region come under attack, driving up the global price of fuel and any item that requires shipping.

On Wednesday, the US military said it had attacked five oil tanker ships with ties to Iran. Tehran, in response, launched attacks on two US Navy destroyers and eight oil tankers in the Strait of Hormuz, causing "heavy damage" to the vessels, according to Iranian state media.

A day earlier, the Iran-linked Houthis in Yemen launched a wave of attacks in Saudi Arabia, sparking fires at oil facilities.

The fighting, which began again recently after a 60-day ceasefire between the US and Iran formally expired last month, has also raised predictions that the rising fuel costs could lead to higher interest rates in the US.