Iran has sent two warships to the waters off Yemen while the US has accelerated moves to supply weapons to the Saudi coalition as foreign powers get drawn deeper into the conflict.

The Alborz destroyer and Bushehr support vessel sailed from Bandar Abbas to the Gulf of Aden today with military bosses claiming the move is designed to protect Iranian shipping from piracy.

It comes as Saudi Arabia continues to lead a bombing campaign to oust the Iran-allied Houthi movement which has taken most of Yemen and forced President Abd-Rabbu Mansour Hadi to flee to Riyadh.

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Smoke billows from a Saudi-led airstrike on Sanaa, Yemen earlier today amid reports Iran has sent a navy destroyer and another vessel to the Gulf of Aden

Conflict: Yemeni supporters of the southern separatist movement fire towards Houthi rebels during clashes in the northern Dar Saad neighbourhood of the southern Yemeni city of Aden today

A Houthi fighter aims a weapon upwards as smoke rises from a building after a Saudi-led airstrike on a street in Sanaa, Yemen

Saudi Arabia and several Arab allies have imposed an air and naval blockade on Yemen in a two-week campaign that has been condemned by Iran, which has called for dialogue.

The Iranian ships will patrol the Gulf of Aden, south ofYemen, and the Red Sea, Rear Admiral Habibollah Sayyari said in comments cited by Press TV

Meanwhile, Washington deepened its involvement in the conflict as aid agencies scrambled to deliver help to civilians caught up in the campaign now heading into its third week.

The Red Cross has warned of a 'catastrophic' situation in main southern city Aden where militia loyal to fugitive President Abedrabbo Mansour Hadi have been holding out against Houthi Shiite rebels and their allies within the security forces.

Gunfight: A man fires towards Houthi rebels. Eleven people were killed in Yemen's main southern city Aden overnight in clashes between rebels and forces loyal to fugitive President Abedrabbo Mansour Hadi

Scores of people have been killed or wounded in the street fighting in the heart of the port city of Aden

Scores of people have been killed or wounded in the street fighting in the heart of the port city and aid agency Doctors Without Borders said it feared many more had been unable to reach hospitals.

The main Shiite power Iran, which has strongly opposed the Saudi-led intervention, stepped up its efforts for a negotiated settlement with a visit to Saudi ally Pakistan by Foreign Minister Mohammed Javad Zarif.

Islamabad has so far deflected appeals by Riyadh to join the coalition of nine - mainly Sunni - Arab countries intervening in Yemen, for fear of deepening sectarian divisions at home and across the Muslim world.

US Deputy Secretary of State Antony Blinken said Washington was stepping up weapons deliveries and intelligence sharing in support of the Saudi-led coalition.

'Saudi Arabia is sending a strong message to the Houthis and their allies that they cannot overrun Yemen by force,' Blinken told reporters in the Saudi capital.

Firefighters jet water on to a burning building after eyewitness reports that it had been hit in an air strike

A girl runs for shelter during an air strike in Sanaa. Saudi Arabia is leading a bombing campaign to oust the Iran-allied Houthi movement which has taken most of Yemen

'In support of that effort we have expedited weapons deliveries,' he said after talks with Defence Minister Mohammed bin Salman and other Saudi officials.

A US defence official told AFP that Washington was sending primarily precision-guided munitions.

The coalition launched its air war on March 26 as the rebels and their allies closed on Hadi's last refuge Aden, prompting him to flee to neighbouring Saudi Arabia.

Riyadh accuses Tehran of backing the rebels and has vowed to bomb them into surrender to prevent them establishing a pro-Iran state on its doorstep.

But the rebels have powerful allies within the security forces who have remained loyal to longtime strongman Ali Abdullah Saleh, forced from power in 2012 after a year-long, Arab Spring-inspired uprising.

Eight rebels and three loyalist militiamen were killed in clashes in Aden overnight, a military source said.

Saudi-led warplanes also bombed rebel positions at the city's international airport and the huge Al- Anad air base to its north, another military source said.

Bomb site : A man surveys a damaged building hit in an airstrike organised by a Saudi-led alliance

Wreckage: A man inspects the twisted remains of a building hit in an airstrike Sanaa, Yemen

Washington is stepping up weapons deliveries and intelligence sharing in support of the Saudi-led coalition

Al- Anad was a key monitoring post in Washington's longstanding drone war against Al-Qaeda until it withdrew its troops as fighting intensified last month.

Last week, Al-Qaeda seized much of Hadramawt provincial capital Mukalla. On Tuesday, they attacked one of the last loyalist strongholds in the city.

US Defence Secretary Ashton Carter acknowledged on Wednesday that the fighting in Yemen was complicating Washington's counter-terrorism efforts but vowed they would go on regardless.

'Obviously it's always easier to conduct CT ops when there is a stable government willing to cooperate,' he said.

'That circumstance now obviously doesn't exist in Yemen but that doesn't mean that we don't continue to take steps to protect ourselves. We have to do it in a different way, but we do and we are.'

Yemeni fighters opposing the Houthi rebels hold a bullet belt in the northern entrance to Aden as clashes continue to rage in the embattled city

A heavily armed Yemeni fighter walks near the entrance to Aden. The Red Cross has warned of a 'catastrophic' situation in the city

As Iran's top diplomat prepared to visit, Pakistan said it would take its time deciding whether to accept the Saudi request to join the coalition.

Prime Minister Nawaz Sharif said Pakistan was 'not in a hurry' to decide and that diplomatic efforts were under way involving Turkey and Iran.

Turkish President Recep Tayyip Erdogan, who has expressed support for the coalition without providing military forces, held talks in Tehran on Tuesday.

'We both think war and bloodshed must stop in this area immediately and a complete ceasefire must be established and the strikes must stop,' his Iranian counterpart Hassan Rouhani said after their meeting.