Arab leaders at a summit in Egypt will announce the formation of a unified regional force to counter growing security threats, according to a draft of the final communique, as conflicts rage in countries such as Yemen and Libya.

The summit will also call on Iranian-allied Houthi fighters who have made rapid advances in Yemen to leave that country's capital and hand over their arms to "legitimate" authorities, said the draft, obtained by Reuters.

Working out the mechanism and logistics of the unified force, an idea floated by Egyptian President Abdel Fattah Al-Sisi, could take months. Previous similar experiments have failed to produce tangible results in the divided Arab world.

The draft resolution identified the military force as voluntary, meaning no state would be required to take part.

That may give Arab states the flexibility needed for intervention in countries such as Yemen, where Saudi Arabia patched together a 10-nation Arab coalition against Houthi fighters and launched military strikes on Thursday.

Meanwhile, Saudi Arabia's navy evacuated dozens of diplomats from Yemen on Saturday and the UN pulled out international staff after a third night of Saudi-led air strikes trying to stem advances by Iranian-allied Houthi fighters.

Residents reported heavy clashes between the Houthis and mainly Sunni tribal fighters in the south of the country, while the air campaign sought to stall a fresh offensive by the Shi'ite Muslim group on Aden from the east.

Riyadh's intervention, a surprise move, is planned to last a month but could extend for five or six, a Gulf diplomatic source said.

He said satellite imagery had shown in January that the Houthis had repositioned long-range Scud missiles in the north, close to the Saudi border and aimed at Saudi territory. A Yemeni official said Iran, which says it has not armed the Houthis, was providing parts for the missiles.

Eighty-six foreign diplomats and Saudi nationals were shipped out of Aden to the Red Sea port of Jeddah, a Saudi military officer said, escaping the city where President Abd-Rabbu Mansour Hadi had taken refuge until Thursday, when he left for Egypt to shore up Arab support for his crumbling authority.

The director general of Yemen's Health Ministry, Al-Khadher Laswar, said more than 68 people had been killed and 452 wounded in the city since Wednesday. Explosions at Aden's largest ammunition depot on Saturday killed at least 15 people and wounded dozens, he said.

In the capital Sanaa, which has been under Houthi control since September, the United Nations said most of its 100 international staff were evacuated. Airport officials said up to 250 other foreigners working for international oil companies and NGOs also flew out to Ethiopia and Djibouti.

Pakistan, which has yet to decide whether to offer military support to the Saudis, is flying jumbo jets to Yemen to evacuate hundreds of nationals, a Defence Ministry official said in Islamabad on Sunday, after TV pictures showed distraught families pleading for help.

A convoy of 600 Pakistanis was moving towards the Red Sea port of Hodeida, where "arrangements for their brief stay before their return journey to Pakistan have been made", Foreign Secretary Aizaz Chaudhry was quoted by media as saying.

Houthi fighters seeking to overthrow the Western- and Saudi-backed Hadi have continued to make gains since the Saudi-led coalition launched air strikes against them on Thursday.

On Friday, the Houthis and allied army units gained their first foothold on Yemen's Arabian Sea coast by seizing Shaqra, 100 km (60 miles) east of Aden, allowing them to open a new front to march on the south's main city. - Reuters