The United Nations Children's Fund (UNICEF) says nearly 1,400 children have been killed in the ongoing deadly Saudi campaign against Yemen.

Meritxell Relano, UNICEF's representative in Yemen, said on Wednesday that hundreds more had been injured and many schools closed since March 2015, when Saudi Arabia started its campaign.

"Attacks on civilian areas continue to kill and injure scores of children in Yemen," Relano said, adding, "Instead of learning, children are witnessing death, war and destruction."

Relano said the actual casualty toll was likely to be much higher than the verified figures. She said that some 2,000 schools across Yemen can no longer be used because they have been damaged, destroyed or are used as shelters or for military purposes.

Elsewhere in her remarks, the UN official called on all parties in the conflict to stop attacks on schools and protect children.

"Schools have to be zones of peace at all times, a sanctuary where children can learn, grow, play and be safe," Relano said.

"Children should never risk their lives only to attend school."

The plea follows an airstrike by Saudi warplanes near a school in northern Yemen on Tuesday. Medics said the attack killed at least five civilians, including two children.

International organizations and human rights groups have harshly criticized the regime in Riyadh for its airstrikes on Yemen, which have killed and maimed hundreds of children.

UNICEF's representative in Yemen Meritxell Relano looks on during a press conference in the Yemeni capital, Sana'a, January 11, 2017. (Photo by AFP)

The Saudi war has so far killed over 11,400 people, according to the latest tally by a Yemeni monitoring group. The war was launched in an attempt to restore power to Abd Rabbuh Mansur Hadi, a Saudi ally who has resigned as Yemen’s president but seeks to forcefully return to power.

The Yemeni army, backed by Houthi Ansarullah fighters and allied popular forces, has been defending the country against the Saudi aggression.