The Mexican foreign minister says no secret immigration deal exists between Mexico and the US, just hours after President Donald Trump tweeted that a “fully signed and documented” agreement would be “be revealed in the not too distant future.”

Marcelo Ebrard, Mexico’s top diplomat, said in a news conference in Mexico City on Monday that there was an understanding that both countries would evaluate the number of migrants crossing the border of Mexico and the United States in the coming months, according to the New York Times.

If the number is no significantly reduced, Mr Ebrard says, both nations will renew discussions about changes to regional asylum rules. According to American officials, those numbers will be reviewed in 45 days, and again in 90 days.

This plan for assessment of the situation before coming to a new arrangement directly contradicts a tweet sent by Mr Trump early Monday morning.

“We have fully signed and documented another very important part of the Immigration and Security deal with Mexico, one that the US has been asking about getting for many years,” the president wrote.

“It will be revealed in the not too distant future and will need a vote by Mexico’s Legislative body!.." he continued. "We do not anticipate a problem with the vote but, if for any reason the approval is not forthcoming, Tariffs will be reinstated!”

Mr Ebrard said in his own news conference that such an agreement on the asylum changes does not exist.

An agreement announcement last Friday, he said, delayed the discussion needed by the Mexican senate. This gives Mexico time to prove to the president that would reduce the flow of immigration, which he has maintained is a problem.

Mr Ebrard says the understanding negotiators have reached relies on still more research and discussion.

“Let’s have a deadline to see if what we have works and if not, then we will sit down and look at the measures you propose and those that we propose,” he said, describing the ongoing process.

It remains unclear what the president's tweets referred to. He has not yet tweeted a response to Mr Ebrard's conference.