Riyadh (AFP) - Gulf monarchies on Wednesday voiced support for Morocco's claim over Western Sahara during a joint summit in Riyadh, where Moroccan King Mohammed VI spoke of a "dangerous" situation.

"We stress our support to all political and security causes that are important for your brotherly country, mainly the Western Sahara," Saudi King Salman said at the opening of the summit of leaders of the Gulf Cooperation Council and the North African nation.

In addition to Saudi Arabia, the GCC includes Bahrain, Kuwait, Oman, Qatar and the United Arab Emirates.

King Salman stressed the GCC's "categorical rejection of any harm to the interests of Morocco" over the disputed territory, where the Algiers-backed Polisario Front demands independence.

Morocco's monarch urged Gulf monarchies to stand by his country to protect it from "plots against its territorial integrity," adding that the UN Security Council's annual Western Sahara discussions in April were being used "to blackmail Morocco".

He accused UN chief Ban Ki-moon of being used in a "war by proxy" against Morocco through his "biased statements".

"The situation is dangerous this time. It is unprecedented in the dispute" over the desert territory, he said.

Morocco was infuriated when Ban last month referred to the "occupation" of Western Sahara during a visit to a Sahrawi refugee camp in Algeria.

Morocco rejected an explanation from Ban's office that his remarks were not deliberate and that he regretted the "misunderstandings."

The United Nations has been trying to broker a Western Sahara settlement since 1991 after a ceasefire was reached to end a war that broke out when Morocco deployed its military in the former Spanish territory in 1975.

Local Sahrawi people are campaigning for the right to self-determination, but Morocco considers the territory as part of the kingdom and insists its sovereignty cannot be challenged.

Morocco is a close ally of Saudi Arabia.

In 2011, the GCC had proposed that Morocco and Jordan, both fellow monarchies, join the bloc. The project failed but the organisation set up a $5-billion fund for the two countries.

Morocco is a member of the Saudi-led Arab coalition fighting Iran-backed Shiite rebels in Yemen, where it lost an F16 warplane in March 2015.