Saudi-led air raids have killed 21 civilians in Yemen's capital Sanaa only two days into the start of a United Nations-brokered truce that Saudi Arabia has said it does not recognise.

"Three missiles targeted the neighbourhood, destroying 15 houses and killing 21 people and wounding 45 others," one Sanaa resident said.

A Saudi-led Arab coalition has been bombing the Houthi militias since March in a bid to restore to power to Yemen's exiled president Abdrabbuh Mansour Hadi, who has since fled to Riyadh.

The UN-brokered a pause in the fighting between warring factions on Friday to allow humanitarian aid to be delivered, but the Saudi-led coalition said it had not been asked by Yemen's exiled president to stop its raids in whose name they say they are acting.

Brigadier-General Ahmed al-Asiri, the spokesman of the Arab coalition, has said there would be no truce because Houthis were not committed to a ceasefire and no UN observers had been deployed on the ground to monitor possible violations.

But Saleh al-Samad, a Houthi leader, described the continued Saudi raids as presenting "a clear challenge to the international community to shoulder its responsibilities and seriously try to stop this aggression".

The Houthis, who are allied to Saudi Arabia's regional rival Iran, advanced from their northern stronghold a year ago, capturing the capital Sanaa in September and then pushing south early this year, prompting the Saudi-led airstrikes.

More than 3,000 people have been killed in the fighting and air strikes so far, amplifying an existing humanitarian crisis.

Saudi has said it does not recognize the UN-brokered truce as it had not been requested by Yemen's exiled president. ( Reuters: Mohamed al-Sayaghi )

Reuters