The UN health agency on Saturday said it had delivered eight tonnes of medications to hospitals in Taiz, the third-largest city under siege in Yemen's war.

It marked the first time since the start of the conflict that the United Nations negotiated access by direct route to Taiz, crossing Yemen's frontline to distribute the vital medical supplies, the World Health Organisation said in a statement.

"The truck arrived in Taiz City yesterday. The medicines have been distributed to hospitals today," WHO spokesman Tarik Jasarevic told AFP.

The shipment contained trauma kits, emergency medicine, various types of intravenous fluids and pneumonia kits.

More than 350,000 people are in need of urgent medical aid in Taiz, where pro-government forces are fighting back a rebel assault, the Geneva-based agency said.

Jasarevic added that the UN had previously only been able to get some medical supplies to Taiz via smaller, side roads in the war-ravaged country.

Yemen this month marks two years since a Saudi-led Arab coalition intervened in support of government troops in the conflict.

UN mediation efforts and seven ceasefire accords have failed to end the war, which has so far left more than 7,500 people dead and 40,000 wounded.