US President Donald Trump has continued to rage over immigration, calling on Congress to pass border legislation using the "nuclear option if necessary".
Mr Trump tweeted that the US must build a border wall, but argued that "Democrats want No Borders, hence drugs and crime!"
DACA is dead because the Democrats didn’t care or act, and now everyone wants to get onto the DACA bandwagon... No longer works. Must build Wall and secure our borders with proper Border legislation. Democrats want No Borders, hence drugs and crime!— Donald J. Trump (@realDonaldTrump) April 2, 2018
He also said that a deal to help "Dreamer" immigrants is "dead because the Democrats didn't care or act".
Mr Trump has previously called for the "nuclear option" - changing Senate rules to end the filibuster.
But Senate Majority Leader Mitch McConnell has dismissed that option in the past, saying Republicans will welcome the filibuster when they return to being the Senate minority.
The $1.3trn funding package Congress passed last month included $1.6bn in border wall spending.
But much of that money can only be used to repair existing segments, not build new sections.
Congress also put restrictions on the types of barriers that can be built.
Mr Trump began tweeting over the weekend on immigration from Florida, threatening to pull out of a free trade agreement with Mexico unless it does more to stop people from crossing into the US.
He claimed they are coming to take advantage of protections granted to certain immigrants.
Mr Trump said Mexico must "stop the big drug and people flows, or I will stop their cash cow, NAFTA. NEED WALL!"
Mexico is doing very little, if not NOTHING, at stopping people from flowing into Mexico through their Southern Border, and then into the U.S. They laugh at our dumb immigration laws. They must stop the big drug and people flows, or I will stop their cash cow, NAFTA. NEED WALL!— Donald J. Trump (@realDonaldTrump) April 1, 2018
The US, Canada and Mexico are participating in tense negotiations over the North American Free Trade Agreement at Mr Trump's insistence. The president says NAFTA is bad for the US.
"Mexico has got to help us at the border," Mr Trump, holding his wife's hand, told reporters before the couple attended Easter services at an Episcopal church near his home in Palm Beach, Florida.
Former president Barack Obama created the Deferred Action for Childhood Arrivals programme to provide temporary protection and work permits to hundreds of thousands of immigrants who are living in the US illegally after being brought here as children.
Mr Trump ended the programme last year but gave Congress six months to pass legislation enshrining it.
A deal has so far proved elusive and Mr Trump has blamed Democrats.
It was not immediately clear what Mr Trump was referring to when he said people are coming to take advantage of the programme.
The Department of Homeland Security is not issuing new permits, though existing ones can be renewed.
The Obama administration allowed sign-ups during a set period of time, and the programme is closed to new entrants.
Proposed DACA deals crafted by politicians and rejected by Mr Trump were also not open to new participants.
The president did not explain what he meant when questioned by reporters as he entered the Church of Bethesda-by-the-Sea with the first lady and his daughter Tiffany.
Mr Trump, when addressing reporters briefly before entering the church, again blamed Democrats for failing to protect the Dreamers.
"They had a great chance. The Democrats blew it. They had a great, great chance, but we'll have to take a look because Mexico has got to help us at the border. They flow right through Mexico. They send them into the United States. It can't happen that way anymore."
Mr Trump promised during the 2016 presidential campaign to build a southern border wall to stop illegal immigration and drugs from Mexico, but Congress has frustrated him by not moving as quickly as he wants to provide money for construction.
The president also complained on Twitter that border patrol agents cannot do their jobs properly because of "ridiculous liberal (Democrat) laws" that allow people caught for being in the country illegally to be released while they await a hearing before a federal immigration judge.
Border Patrol Agents are not allowed to properly do their job at the Border because of ridiculous liberal (Democrat) laws like Catch & Release. Getting more dangerous. “Caravans” coming. Republicans must go to Nuclear Option to pass tough laws NOW. NO MORE DACA DEAL!— Donald J. Trump (@realDonaldTrump) April 1, 2018
Mr Trump tweeted that the situation is "Getting more dangerous" and "Caravans" are coming.
Mexico has the absolute power not to let these large “Caravans” of people enter their country. They must stop them at their Northern Border, which they can do because their border laws work, not allow them to pass through into our country, which has no effective border laws.....— Donald J. Trump (@realDonaldTrump) April 2, 2018
The president's tweets came after Fox News's Fox & Friends reported early on Sunday on what it said is a group of 1,200 immigrants, mostly from Honduras, headed to the US.
The segment was a follow-up to a report by BuzzFeed News on hundreds of Central Americans making their way through Mexico in the hope that American authorities will grant them asylum or be absent when they attempt to cross the border.
The Fox headline was: Caravan of illegal immigrants headed to US. The president is known to watch the cable TV programme in the morning.
Brandon Judd, leader of the union representing border patrol agents, predicted on Fox & Friends that those in the caravan would create havoc and chaos in the US as they wait for what he described as immigration reform.
Mr Judd also said Congress needs to pass tougher laws, an idea Mr Trump appeared to echo, and create more bed space for immigration authorities to house people.
Ohio governor John Kasich chided Mr Trump over the tone of the tweets.
"A true leader preserves & offers hope, doesn't take hope from innocent children who call America home. Remember, today is Easter Sunday," tweeted Mr Kasich, a Trump critic who challenged him for the 2016 Republican presidential nomination.
Arizona Republican Senator Jeff Flake, another Trump foe, urged Congress to take up the fight for Dreamers.
"There are plenty of lawmakers on both sides of the aisle who stand ready to work with the administration on legislation to protect DACA kids who call America home," he tweeted. "Let's do it."