Iran's Revolutionary Guard says four oil tankers have exploded and caught fire in the Strait of Hormuz after straying onto routes it calls off limits. The claims landed on the same day oil prices climbed to their highest level since late April.

None of the Iranian accounts could be independently confirmed. It was also unclear when each blast took place or which flags the tankers flew.

What Iran is claiming

In its latest statement the Guard's navy said a fourth tanker loaded with more than 2 million barrels of crude struck a mine and was left burning after a powerful blast. An earlier statement had said a different tanker with a similar load also hit a naval mine.

Iranian officials said the first three ships had shut off their radar and navigation gear and brushed aside warnings from Guard patrols as they tried to use the southern lane near the coast of Oman. Tehran treats that corridor as unauthorized and says it is mined. The regular Iranian army reported a separate tanker fire east of the strait.

A rare limpet mine attack

One strike has been confirmed by outside monitors. A British maritime security agency said a small boat pulled alongside a tanker about 25 nautical miles northeast of Khasab in Oman on Thursday night. Its crew fixed two explosive charges to the hull above the waterline.

The blasts set off a fire in the engine room and briefly knocked the ship out of action. The agency said the fire is out, the crew is safe and there was no pollution. The vessel went on to its next port.

Maritime security firms identified the ship as the Panama-flagged Louise 1. They called it the first successful limpet mine attack in the waterway since the war with Iran began in February. A similar attempt in September failed when the charges did not go off.

The same monitors logged other trouble nearby. A crude tanker was hit by an unknown projectile as it left the strait. A second ship was struck about 40 nautical miles south of Lavan Island and caught fire with no injuries reported. A small trading dhow burned and sank after its crew was taken off.

The U.S. pushes back

Iran also said it shot down and captured an American MQM-170 drone near Qeshm Island and destroyed an unmanned U.S. boat. U.S. Central Command rejected the boat claim. It said every American unmanned surface vessel in the region is accounted for, including a squadron of sea drones now patrolling the strait.

The command has insisted for weeks that mines have been swept from the main shipping lanes. A Guard spokesman dared Washington to back up that claim with independent evidence. Central Command said last weekend it has helped Gulf states move 1.5 billion barrels of oil through Hormuz since the summer while the U.S. keeps up its blockade of Iranian ports.

Why drivers will notice

Brent crude for December delivery rose about 2.5% to $117.75 a barrel in early afternoon trading after touching $118. U.S. benchmark crude gained 2.7% to $104.79. Both are headed for a fourth straight monthly gain with Brent up about 13% for October and U.S. crude up about 15%.

Fuel futures moved too. Diesel futures rose more than 11 cents to about $4.85 a gallon while gasoline futures added roughly 7 cents to near $3.26.

Traders say they are bracing for a possible new round of fighting once the U.S. midterm elections are over on Nov. 3. Qatari mediators returned to Tehran on Friday to keep talks between Washington and Iran alive.

About a fifth of the world's oil normally moves through the narrow strait. Traffic has been tightly squeezed since U.S. and Israeli strikes on Iran opened the war at the end of February.