SANAA -- International Committee of Red Cross (ICRC) said Tuesday that 40 children were among 51 people killed in a recent airstrike on a school bus in Yemen's northern province of Saada.

There are also 56 children among the 79 people injured in the strike, Johannes Bruwer, head of the ICRC delegation in Yemen, said in an emailed statement.

"Final information issued by Saada authorities: out of a total number of 130 victims, 51 are dead, including 40 children, and out of the 79 injured, 56 are children. The numbers speak for themselves," the statement said.

On Thursday, two airstrikes hit a school bus in the Dhahyan market in Saada, the key stronghold of the Iran-allied Shiite Houthi rebels.

The Houthi rebels blamed the Saudi Arabia-led coalition for the attack, which has triggered popular anger across Yemen and condemnation from international humanitarian agencies.

UN Secretary-General Antonio Guterres condemned the airstrike on the school bus, calling for an "independent and prompt investigation."

The ICRC also condemned the airstrikes, saying "civilians must be protected during conflict under international humanitarian law."

On Friday, the Saudi-led coalition said it would investigate the airstrike. But on Saturday, the Saudi mission to the UN submitted a letter to Guterres affirming that the airstrike was "legitimate and it targeted Houthi leaders responsible for recruiting and training young children."

On Monday, thousands of Yemeni mourners from several northern provinces attended the funeral in Saada, where the killed children were buried.

Local residents said the students were traveling on a field trip when their bus was hit in the Dhahyan market.

The chief of Houthi revolutionary committee, Mohammed Ali al-Houthi, attended the funeral and accused the United States of backing the coalition airstrikes.

The U.S. State Department has reportedly urged the Saudi-led coalition to "conduct a thorough and transparent investigation".

Yemen has been locked in a civil war since the Houthi rebels overran much of the country and seized all northern provinces in late 2014, including the capital Sanaa.

Saudi Arabia is leading an Arab military coalition that intervened in the Yemeni war in 2015 to support the government of exiled President Abd-Rabbu Mansour Hadi.

More than 10,000 Yemenis, mostly civilians, have been killed in the war, with about 3 million others displaced.