"Mexico was not being cooperative on the Border in things we had, or didn't have, and now I have full confidence, especially after speaking to their President yesterday, that they will be very cooperative and want to get the job properly done," Trump said on Twitter.
"Importantly, some things not mentioned in yesterday press release, one in particular, were agreed upon. That will be announced at the appropriate time," he added. He did not elaborate on what that matter was.
The deal, announced on Friday after three days of negotiations in Washington, averted Trump's threatened imposition of 5% import tariffs on all Mexican goods starting on Monday. The agreement expands a controversial program that sends migrants seeking asylum in the United States to Mexico while their cases are being processed and boosts security at Mexico's southern border.
Trump also pushed back at a New York Times report that the deal consisted of commitments previously agreed by Mexico, calling it a "false report."
Citing officials from both countries familiar with the negotiations, the newspaper said on Sunday that the expansion of the program to allow asylum-seekers to remain in Mexico was reached in December.
The newspaper also said Mexico agreed in March to deploy its National Guard throughout the country, giving priority to the southern border.
"We have been trying to get some of these Border Actions for a long time, as have other administrations, but were not able to get them, or get them in full, until our signed agreement with Mexico," Trump wrote on Twitter.