The announcement on Tuesday, which raises further doubts over Ukraine’s participation in the bid, was made through a statement signed by King Mohammed VI and read at a meeting of the Confederation of African Football.
A spokesman for the Spanish football federation told AFP it would meet with its Portuguese and Moroccan counterparts in Kigali on Wednesday, but made no mention of Ukraine.
“The presidents will announce any news regarding the candidacy for the 2023 World Cup in Kigali,” the spokesman added.
Spain and Portugal declared their joint candidacy in 2021, before adding Ukraine to their bid last October.
In contrast to the distance between Ukraine, and Spain and Portugal, Morocco is separated from Spain only by the Strait of Gibraltar.
A South American bid including Uruguay, Argentina, Paraguay and Chile is set to challenge the Iberian bid, and Saudi Arabia hopes to lead a joint ticket with Egypt and Greece.
The World Cup has had joint hosts before.
In 2002 Japan and South Korea shared the competition. In 2026, the finals will be played in the United States, Mexico and Canada, when 11 of the 16 planned venues will be in the US.
The 2026 World Cup will expand from 32 teams to 48 and, under the format FIFA announced on Tuesday, will stretch to 104 matches, up from 64 in Qatar last year.
Morocco was the other candidate for 2026 but finished a distant second in the voting.
That was the fifth time Morocco had bid to host the finals after trying for 1994, 1998, 2006 and 2010 World Cups.
Morocco had already said it planned to bid for the 2030 World Cup, which has been held in Africa once, in South Africa in 2010.
“This candidature will be a gathering of the best on both sides, and the demonstration of an alliance of genius, creativity, experience and means,” said King Mohammed in his message, read by the Moroccan Minister of Sports Chakib Benmoussa.
At the last World Cup, in December in Qatar, Morocco became the first nation from either Africa or the Arab world to reach the semi-finals.
The first World Cup, in 1930, was hosted and won by Uruguay, which is making a joint bid with Argentina, Paraguay and Chile.