ADEN -- The United Nations is beefing up its inspections of ships bringing humanitarian aid to Yemen to ensure that no military items are being smuggled and to speed up delivery of desperately-needed relief supplies, UN and Saudi officials say.

The move comes as the armed Houthi movement controlling much of northern Yemen steps up attacks on the kingdom, hitting a Saudi oil tanker on Tuesday.

The Arab coalition said overnight that Riyadh's air defense had intercepted a missile aimed at Jazan city.

Saudi Arabia accuses Iran of supplying missiles to the Houthis, who have taken over the Yemeni capital Sanaa and other parts of the country. Tehran and the Houthis deny the allegation.

Under an arms embargo imposed by the UN Security Council, monitors from the UN Verification and Inspection Mechanism (UNVIM) are based in ports in Djibouti, Dubai, Jeddah and Salalah to observe screening of cargo destined for Yemen.

"We met with the UNVIM director and his team in Riyadh and we agreed on improved and enhanced capability," Saudi Ambassador to Yemen Mohammed S. al-Jabir told reporters in Geneva on Wednesday.

He said UNVIM would increase its inspectors to 10 from four and its monitors to 16 from six and would also improve its technology to inspect ships.

The team supporting Lise Grande, the UN Humanitarian Coordinator in Yemen, confirmed on Thursday the steps taken to increase the number of monitors and inspectors and the use of scanning equipment.

A major UN conference on Yemen was held this week, drawing pledges of more than $2 billion toward a $3 billion UN humanitarian appeal.

Saudi Arabia and the United Arab Emirates have contributed $930 million.

"We are cooperating with the UNVIM and other UN organizations to facilitate and to increase the number of ships that arrive at Hodeidah port," Jabir said, referring to Yemen's main port for humanitarian and commercial goods, under Houthi control.

UNVIM only checks commercial and aid ships going to northern ports under Houthi control - Hodeidah, Salif and Ras Isa - and not to Aden, which is under government control.

Yemen, the Arabian peninsula's poorest country, is reeling from the world's worst humanitarian crisis where 22 million people need vital assistance.

When the Houthis fired missiles at Riyadh last November, the Western-backed coalition shut Yemen's airports and ports.

Saudi Arabia's permanent mission to the UN sent a letter to the UN's Secretary-General, Antonio Guterres, and the President of the Security Council calling for the need for Yemen's Hodeidah port to be placed under international supervision.

They also called for the reprimanding of the Houthi militia and Iran for violating international laws. They called on the UN to take the necessary measures to implement Security Council resolutions 2216 and 2231, stressing that the coalition will continue to secure international navigation in Bab al-Mandab and the Red Sea.

This comes following a Houthi attack on a Saudi oil tanker in Hodeidah on Tuesday. The Arab Coalition's spokesman, Colonel Turki al-Malki, had confirmed that at exactly 1:30 pm local time, a Saudi oil tanker was attacked in international waters west of Hodeidah port, currently controlled Houthi armed militias supported by Iran.

The planned attacked was foiled following the intervention of a coalition naval ship.

Maliki said on Wednesday that the coalition successfully targeted Houthi labs that manufacture booby-trapped boats in Hodeidah, adding that the militia has turned the port into a storage space for weapons.

He added that the coalition is securing international navigation in order for humanitarian aid to enter, where more than two million Yemenis have already benefited from this flow of aid.

Maliki welcomed the international condemnation of Houthi attempts to target navigation, as well as firing of ballistic missiles at Saudi Arabia.