The US sailors and Marines entered the Red Sea on Sunday after transiting through the Suez Canal in a pre-announced deployment, the US Navy's Fifth Fleet said in a statement.

They arrived on board the USS Bataan and USS Carter Hall warships, providing "greater flexibility and maritime capability" to the Fifth Fleet, the statement added.

The US military says Iran has either seized or attempted to take control of nearly 20 internationally flagged ships in the region over the past two years.

USS Bataan is an amphibious assault ship which can carry fixed-wing and rotary aircraft as well as landing craft. The USS Carter Hall, a dock landing ship, transports Marines, their gear, and lands them ashore.

"These units add significant operational flexibility and capability as we work... to deter destabilising activity and deescalate regional tensions caused by Iran's harassment and seizures of merchant vessels," Fifth Fleet spokesman Commander Tim Hawkins told AFP.

The deployment comes after Washington said its forces blocked two attempts by Iran to seize commercial tankers in international waters off Oman on July 5.

The maritime services in Iran said one of the two tankers, the Bahamian-flagged Richmond Voyager, had collided with an Iranian vessel, seriously injuring five crew members, according to state news agency IRNA.

In April and early May, Iran seized two oil tankers within a week in regional waters.

Those incidents came after Israel and the United States blamed Iran in November for what they said was a drone strike against a tanker operated by an Israeli-owned firm carrying gas oil off the coast of Oman.

The US announced last month that it would deploy a destroyer, F-35 and F-16 warplanes, along with the Amphibious Readiness Group/Marine Expeditionary Unit, to the Middle East to deter Iran from seizing ships in the Gulf.

Last week, a US official told AFP that Washington is also preparing to deploy Marines and Navy personnel aboard commercial tankers transiting the Gulf as an added layer of defence.