SANAA: Heavy fighting continued to rage Wednesday near the strategic Red Sea strait of Bab al-Mandab in western Yemen, leaving dozens dead and wounded, security officials said.

Since Monday, fighters aligned with Yemen's internationally recognised President Abed Rabbo Mansour Hadi have been making advances and seizing more territory from Yemen's Houthi rebels, the officials said. Warplanes from the Saudi-led coalition provided air cover for Hadi's forces, they said, speaking on condition of anonymity because they were not authorised to speak to the media.

The war in Yemen is entering its second year after Houthis seised the capital Sanaa and forced Hadi to flee the country. The Saudi-led coalition has waged an extensive air campaign since March 2015 aimed at restoring Hadi's government. The northern region remains under Houthi control.

In Sanaa, officials and witnesses said that two airstrikes hit a gas station near a school in the Nihm district outside Sanaa, the capital. The airstrikes killed at least six civilians including children. They said that the school itself wasn't targeted in Tuesday's airstrikes.

Meritxell Relaño, the UNICEF representative in Yemen, condemned the attacks, saying that one child was confirmed dead and four others were wounded.

The coalition has come under heavy criticism by international rights groups for carrying out attacks against civilians including schools, markets, hospitals and residential areas. More than 4,200 civilians have been killed and the fighting has left more than three million people displaced.

Relaño said in a Wednesday statement that a total of 1,400 children have been killed and more than 2,140 wounded since the war started. She added that 1,400 were recruited by the warring parties. Over 2,000 schools are no longer being used because they were destroyed, used as shelters for the displaced, or occupied by fighters and used for military purposes.

"Schools have to be zones of peace at all times, a sanctuary where children can learn, grow, play and be safe. Children should never risk their lives only to attend school," she said.