With 10 weeks until Saudi Arabia's term on the 15-member Security Council was due to start - on January 1 - UN diplomats do not appear to be in a rush to fill the vacancy and some are hoping Riyadh might still change its mind.

"One waits to see what will happen," British UN Ambassador Mark Lyall Grant said on Tuesday.

The Arab group of countries at the United Nations urged Saudi Arabia on Saturday to reconsider its decision to renounce the rotating seat on the council in protest at the body's failure to end the war in Syria and act on other Middle East issues.

Saudi Arabia was the Arab candidate from the Asia-Pacific bloc. Kuwait had put its hand up to be the next Arab candidate from the group and run for the 2018-2019 term on the Security Council, which has led some diplomats to speculate that the Persian Gulf US ally could be a capable replacement.

Saudi Arabia's decision on Friday to turn down the two-year term has diplomats and officials scratch their heads over what formal notification is needed to begin the process of deciding an alternative candidate.

"There is no agreed procedure because this is the first time that it has happened," said French UN Ambassador Gerard Araud. "It will be done in a few weeks I think. It will take time."

The Security Council is dominated by its five permanent members - Britain, China, France, Russia and the United States - which have veto power over its decisions.

To ensure diversity, the council's 10 elected members are made up of three members from Africa, two from Asia-Pacific, one from Eastern Europe, two from the Latin American and Caribbean group, and two from the Western European and others group. Five are chosen each year to serve two-year terms.

Arab states are split between the Asia-Pacific and African regional blocs and there is an unofficial deal that at least one Arab nation is always represented on the Security Council.

NTJ/BA