RIYADH (Reuters) - The World Food Programme (WFP) says communications equipment that Saudi Arabia stopped from entering Yemen on one of its chartered ships last week, fearing it was meant for the Houthi militia, belonged to the United Nations.

Saudi Arabia is leading an Arab coalition in a war against the Houthis and army forces loyal to former president Ali Abdullah Saleh in March in an effort to restore President Abd-Rabbu Mansour Hadi to power.

It has imposed a naval blockade to stop weapons being imported and was reported in Arab media on Monday as saying the communications equipment had been meant for the Houthis.

The Mainport Cedar, which the U.N. humanitarian organisation said was carrying a cargo of humanitarian relief supplies bound for the Houthi-controlled port of Hodeida, was diverted by the coalition to the Saudi port of Jizan on Feb. 11.

Brigadier General Ahmed Asseri, the coalition's spokesman, said the communications equipment was similar to that used by the Houthis, had been discovered on the ship during an inspection and had not been declared by the WFP.

"It sustains the militias in their combat. Why did they not declare it? We ask them please 'review your procedures, review your personnel' to make sure this does not happen again," he said by phone.

The vessel was carrying a container of medical supplies from the Netherlands and two containers of food from Iran, and had originated its journey in the Iranian port of Bandar Abbas, Asseri said.

"WFP has been asked by the coalition forces to resubmit the paperwork regarding the humanitarian IT equipment," Abeer Etefa, senior spokesman for the WFP said by email.

The equipment included computers, satellite dishes, solar panels, encryption systems, individual communication devices and other material often used for military purposes and found by Saudi forces in Houthi bases on the Saudi border, Asseri said.

Saudi Arabia, which had imposed a blockade on Yemeni ports as part of its campaign, accuses Iran of supplying the Houthis with weapons. Iran denies involvement in the conflict.

In September, the coalition said it had seized an Iranian fishing boat carrying 18 anti-armoured Concourse shells, 54 anti-tank shells, shell-battery kits, firing guidance systems, launchers and batteries for binoculars destined for the Houthis.

Nearly 6,000 people have been killed in Yemen since Saudi-led forces began military operations in Yemen in March last year after the Houthis advanced on Hadi's temporary headquarters in the southern port city of Aden.

(Reporting By Angus McDowall and Sami Aboudi)