US President Donald Trump put Democratic congressional leaders on notice Friday that he would not back relief for Deferred Action for Childhood Arrivals (DACA) beneficiaries unless lawmakers appropriated funds to pay for his proposed wall on the Mexican border.

Nearly 800,000 undocumented young people, known as "Dreamers," have been shielded from deportation since then-President Barack Obama instituted DACA in 2012.

Trump announced in September that he would end DACA in March 2018 and urged Congress to use the six-month grace period to pass legislation addressing the situation of the Dreamers.

"The Democrats have been told, and fully understand, that there can be no DACA without the desperately needed WALL at the Southern Border and an END to the horrible Chain Migration & ridiculous Lottery System of Immigration etc," the president said Friday on Twitter.

"We must protect our Country at all cost!," Trump treated from his Mar-a-Lago club in Palm Beach, Florida, where he is spending the holidays.

Democrats had threatened to block a spending bill needed to keep the government running if the text did not include some kind of fix for DACA, but they ultimately dropped the demand, spurring criticism from immigrants' rights activists.

Trump, who made the proposed border wall a centerpiece of his 2016 campaign, has yet to persuade Congress to appropriate funds to build the barrier.

Democrats are united in opposition to the plan and even some of Trump's fellow Republicans have expressed concern about the cost.

Meanwhile, Trump's continuing push for the wall - and his insistence that Mexico will somehow be made to pay for it - have brought US relations with its southern neighbor to the lowest point in decades.