A UN report says civilian causalities have mounted since the start of the Saudi-led offensive against Shiite rebels in Yemen, with at least 115 children killed.

The UN High Commissioner for Human Rights spokesman Rupert Colville said 1,185 civilians were injured between March 26, when the air strikes began, and April 22.

The air strikes have continued with planes bombing civilian sites suspected of being used by Shiite rebels, also known as Houthis, to store weapons or deploy troops.

Witnesses say a stadium and small villages near the southern town of Zinjibar were bombed.

In the town of Lahj, coalition planes bombed a court house, the headquarters of police commandos and farmland near the airport in the city of Aden.

The UNHCR said more than 500 civilians had been killed.

The deaths resulted from air strikes and armed conflict on the ground between the Houthis and their allies on one side and tribesmen and militias on the other.

The two sides have been engaged in heavy battles in several cities, particularly in the south.

In one incident, the agency said, a bridge was hit twice by planes on April 22 in the western province of Ibb, killing 40 civilians, including seven children. The deaths included people killed while rushing to help casualties of the first strike.

Another large incident was in Sanaa, the capital, where bombings of Fag Atan mountain, which houses the capital's largest weapon depot, flattened houses and killed at least 20 civilians, the rights office said.

The bombings also partially damaged a number of UN offices, including the office of the High Commissioner for Human Rights in Yemen. A day after the strike, medical officials gave an updated toll from the blast, saying 38 civilians were killed.

On March 31, Human Rights Watch said a diary factory came under attack by Saudi air strikes, with 31 workers killed in the western port city of Hodeida.

Saudi Arabia said earlier this week it was suspending the strikes but they resumed within hours.