Mexico has agreed to take "unprecedented steps" to limit illegal immigration to the US.
It is in order to avoid trade tariffs recently threatened by the US president.
Overnight, Donald Trump revealed that a deal had been reached to suspend the tariffs "indefinitely".
In a pair of tweets, he said Mexico's steps would "stem the tide of migration" to the US-Mexico border.
He added: "This is being done to greatly reduce, or eliminate, illegal immigration coming from Mexico and into the United States."
According to a joint declaration published by the US State Department, Mexico will deploy its National Guard throughout the country - giving priority to its own southern border.
Mexican authorities are also pledging "decisive action" to dismantle human smuggling and trafficking groups.
The US says people crossing the border to seek asylum will be rapidly returned to Mexico, "where they may await the adjudication of their asylum claims".
Mexico will allow the returning migrants in on "humanitarian grounds... [offering] jobs, healthcare and education according to its principles".
US officials, meanwhile, say they'll speed up the processing of asylum claims.
The declaration adds: "The United States and Mexico commit to strengthen bilateral cooperation, including information sharing and coordinated actions to better protect and secure our common border."
The Trump administration has frequently focused on its efforts to limit illegal immigration at its border with Mexico - most infamously through the US president's campaign pledge to build a border wall.
In late May, Trump took to Twitter to claim the US would impose a 5% tariff on all goods coming from Mexico from June 10th - adding that the tariffs would gradually increase until illegal immigration 'stopped'.
His administration is already embroiled in an ongoing trade dispute with China.