At least 18 Saudi soldiers were killed in an attack by Houthi militias on a Saudi military site near the border with Yemen, a pro-Houthi television channel reported on Thursday.

Al-Massira television channel reported that Houthi militants and allied tribesmen attacked a Saudi military site adjacent to the outskirts of the northern Saada province, considered the Houthis' stronghold in Yemen.

The broadcaster did not, however, report the time of the attack. The Saudi-led coalition has yet to respond to the allegations.

The channel said that the Houthis destroyed a large amount of military equipment belonging to the Saudi army and launched rockets at a number of other military sites straddling the border with Saada.

If confirmed, the death toll on the Saudi side would be the highest since the Saudi-led coalition began its aerial campaign against Houthi militias and supporters of former president Ali Abdullah Saleh on 25 March.

In a seperate incident, Saudi shells hit an international humanitarian aid office in northern Yemen on Thursday, a local official told Reuters. Five Ethiopian refugees were killed and 10 wounded, the official added. The Saudi-led coalition has also not commented on the reports, although back in March the coalition struck another IDP camp, killing dozens.

Fractious Yemen has remained in turmoil since last September, when the Houthis overran the capital Sanaa, from which they have sought to extend their influence to other parts of the country.

On Wednesday, the UN said that fresh peace talks would take place in Geneva on 28 May. However, Yemen's President Abd Rabbuh Mansour Hadi, who fled to Saudi Arabia in March, has said that he will only attend the talks if the Houthis pull back from several key positions in southern Yemen, something which they have thus far been reluctant to do.

The Houthis have denounced the offensive as unwarranted "Saudi-American aggression" against Yemen.