Thousands of US marines reach Red Sea after Iran tensions

The deployment adds to a growing US military buildup in tense Gulf waterways vital to the global oil trade and led Tehran on Monday to accuse the US of inflaming regional instability.

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.

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 from the Bahrain-based command added.

The deployment adds to efforts "to deter destabilising activity and de-escalate regional tensions caused by Iran's harassment and seizures of merchant vessels," Fifth Fleet spokesman Commander Tim Hawkins told AFP.

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.

In a Monday news conference, Iran's foreign ministry spokesman Nasser Kanani said US deployments are only serving Washington's interests.

"The US government's military presence in the region has never created security. Their interests in this region have always compelled them to fuel instability and insecurity," he told reporters.

"We are deeply convinced that the countries of the Persian Gulf are capable of ensuring their own security."

The spokesman for Iran's Revolutionary Guards, Ramazan Sharif, meanwhile said the Islamic republic "has reached a level of strength and power that can reciprocate any vicious act by the US, such as seizing ships", according to state news agency IRNA.