Iran has increased its supply of weapons to Shia Houthi rebels in war-torn Yemen, as the Trump administration promises a tougher stance on the Islamic Republic (Isis).

Intelligence officials from the US and Iran have told Reuters that the movement of missiles and small arms have been increased to Yemen in recent months, mostly run through Oman.

The increased build-up of arms in the country threatens to prolong Yemen's 19-month-long proxy war in which a Saudi-backed government has battled with Iran-backed Houthi rebels.

The increase in supply comes as relations strain close to breaking point between a new administration in Washington and Tehran. Iran had enjoyed a period of relative rapprochement with the US under previous president Barack Obama however the Trump administration has promised a far tougher stance.

Following the test of a ballistic missile capable of carrying a nuclear payload Trump has imposed sanctions on 26 companies and individuals from around the world that are linked to the firing.

The White House said in a statement as it announced the move that Iran threatens the region by continuing to support terrorism and the development.

The Trump administration signalled its intentions in Yemen when the first military operation authorised by the new administration was sanctioned in the country.

Fourteen al-Qaeda militants were killed in the raid and accompanying drone strike, the Pentagon has said with one Commando killed in the assault. However, the US military has said it is conducting an investigation into the attack after it emerged the raid resulted in a number of civilian casualties.