SANAA - A US aircraft carrier was headed to the Arabian Sea Tuesday as Washington said it was monitoring Iranian vessels suspected of carrying weapons to Yemeni rebels in violation of a UN embargo.

Iran’s regional rival Saudi Arabia, leading the air war on the rebels, meanwhile mobilised its National Guard for operations in Yemen, state media said, without clarifying how the 100,000-strong force would join the campaign. In Geneva, the UN health agency said more than 900 people had been killed in Yemen since late March, when a Saudi-led coalition launched air strikes against the Iran-backed Huthi Shia rebels clashing with pro-government forces.

And the International Organization for Migration announced a temporary suspension of its evacuation efforts due to insecurity. Amid reports of a nine-ship Iranian convoy in the area, the US Navy said it was sending the USS Theodore Roosevelt and guided-missile cruiser USS Normandy “to ensure the vital shipping lanes in the region remain open and safe”.

Yemen risks an imminent collapse in its health system, the UN health agency warned Tuesday, estimating the latest death toll from fighting there at 944.

Another 3,487 people have been listed as injured as of April 17, the World Health Organization said, citing data from medical facilities in Yemen, and stressing that the true numbers were probably higher because many people were unable to reach hospitals for treatment.

The deployment brings to nine the number of US warships in the area, but the Pentagon denied reports they had orders to intercept the Iranian vessels.

Strategically located on key shipping routes and bordering oil-rich Saudi Arabia, Yemen was plunged into chaos last year when the Huthis seized the capital Sanaa.

The coalition of Sunni Arab nations led by Saudi Arabia launched an air campaign against the rebels last month, vowing to restore the authority of President Abedrabbo Mansour Hadi, who fled to Riyadh as the rebels advanced on his southern refuge Aden.

The United States says it is not taking part directly in the strikes, but is providing intelligence and logistical support. Coalition warplanes pressed their air strikes against the rebels and their allies in the security forces overnight, as the civilian death toll from a Monday raid on a missile depot in the capital rose to 38.

A further 532 people were wounded when the twin strikes sparked powerful explosions that flattened nearby houses, medics said.

Rebel spokesman Mohammed Abdulsalam slammed the strikes on the base as a “barbaric crime”, insisting on Facebook that the “aggression will only unite the Yemeni people”.  The coalition says it has carried out more than 2,000 strikes since the start of the campaign, gaining complete control of Yemeni airspace and knocking out rebel infrastructure.

The coalition would continue to impose a naval blockade on Yemen and target any movements by the Huthi Shiite rebel forces. A coalition statement said that the next phase of operations was aimed at resuming the political process in Yemen, delivering aid, and ‘fighting terrorism’ in the country, home to a deadly Al-Qaeda franchise.

The Saudi defence ministry said in a statement that the air strikes had managed ‘to successfully remove threats to Saudi Arabia’s security and that of neighbouring countries’. This, it added, was achieved ‘by destroying heavy weaponry and ballistic missiles which were seized by the Huthi militia and forces allied to (former president) Ali Abduallh Saleh from army bases and camps.’

Meanwhile, Saudi Arabia’s King Salman on Tuesday ordered the Saudi Arabian National Guard, widely regarded as the kingdom’s best equipped military ground force, to take part in Riyadh’s campaign against Iran-allied Houthi rebels in Yemen. Military operations in the campaign have so far been carried out by the Royal Saudi Air Force and the Royal Saudi Land Forces, which answer to the Defence Ministry. The national guard is a separate military structure run by its own ministry.

Iran’s deputy foreign minister said he was optimistic that a ceasefire in Yemen would be announced later on Tuesday, in a sign diplomatic efforts may be underway to stop almost a month of Saudi-led bombing of Yemen’s Houthi group.

Iran has repeatedly called for a halt to an almost month-long campaign of air strikes by Saudi Arabia and Arab allies, but members of the coalition and their Western backers have so far rejected Iran’s proposals, accusing it of supporting the Houthis.

“We are optimistic that in the coming hours, after many efforts, we will see a halt to military attacks in Yemen,” Hossein Amir Abdollahian was quoted as saying by Iranian news agencies.

“Iranian proposals are not being addressed at the moment,” one Yemeni official said on condition of anonymity.