MEXICO CITY -- More top officials could soon follow the foreign minister in quitting to compete for the presidency, President Andres Manuel Lopez Obrador said on Wednesday, as the race to succeed him begins to thin out the government.

Foreign Minister Marcelo Ebrard, one of the favourites to be Mexico's next leader, said on Tuesday evening he would resign next week to focus on his campaign to become the candidate for the ruling leftist National Regeneration Movement (MORENA).

Ebrard made the announcement after months of making the argument that MORENA's presidential hopefuls should step down to ensure a level playing field in the contest to succeed Lopez Obrador, whose term will end on Sept. 30, 2024.

It appears Ebrard is winning that argument, and several aides to the president look poised to follow him soon.

Interior Minister Adan Augusto Lopez also plans to resign next week to focus on his own presidential bid, two government sources told Reuters.

The party is due to hold a board meeting on Sunday to set out the rules for the internal contest.

MORENA party chairman Mario Delgado said after Ebrard's announcement that the presidential contenders would ultimately need to step down to ensure the competition was fair.

If MORENA's board decides that on Sunday, then interior minister Lopez and Mexico City Mayor Claudia Sheinbaum, two other top contenders, would need to resign, Lopez Obrador said at a regular press conference.

So, too, could Ricardo Monreal, MORENA's Senate leader, who has also been bidding for the presidency.

Lopez Obrador made the remark after observing that more contenders could follow Ebrard's lead in the next few days.

Opinion polling has tended to give Sheinbaum a slight edge over Ebrard in the race to capture the nomination. MORENA is strongly favored to win the June 2024 election, polls showed.

Mexican presidents are limited to a single six-year term.

Supporters of Ebrard argue his post does not allow him to focus as much on domestic issues as Sheinbaum and Lopez. The two have not been eager to take up Ebrard's plan to have candidates step down from their posts.

Lopez Obrador did not immediately name a replacement for Ebrard, who is due to step down next Monday.

"I have time to think about who can replace him," he said.

Reporting by Dave Graham and Diego Ore; Additional reporting by Stefanie Eschenbacher; Editing by Matthew Lewis, David Gregorio and Grant McCool.