Donald Trump had proposed a "total and complete shutdown of Muslims entering the United States," in December. (File Photo)

Presumptive Republican presidential nominee Donald Trump has warned of a 9/11-like attack on the US if refugees continue to be allowed into the country and alleged that they carry ISIS-funded cell phones."Our country has enough difficulty right now without letting the Syrians pour in," the 69-year-old real estate tycoon told the National Border Patrol Council podcast. On The Green Line podcast, Mr Trump also suggested ISIS is paying for refugees' cell phone plans."They all have cell phones so they don't have money, they don't have anything, they have cell phones. Who pays their monthly charges, right? They have cell phones with the flags, the ISIS flags on them," he alleged."And then we're supposed to say, 'Isn't this wonderful that we're taking them in?' We're led by people that are either incompetent or they don't have the best interest of our country at heart," Mr Trump said.When asked if he thought it would take an attack similar to 9/11 for the country to "wake up about border security," Mr Trump answered in the affirmative."Bad things will happen; a lot of bad things will happen. There will be attacks that you wouldn't believe. There will be attacks by the people that are right now coming in to our country," he warned.Mr Trump also spoke about Hillary Clinton's agenda for immigration reform and his own plans for border control, including his proposal to build a wall at the Southern border with Mexico.The National Border Control agents' union made its first-ever endorsement of a presidential candidate when it backed Mr Trump in March.Mr Trump had proposed a "total and complete shutdown of Muslims entering the United States," in December but just this week he said the ban was "only a suggestion."Mr Trump has also said that he may set up a counter-terrorism commission to study his immigration policies and his controversial proposal to ban foreign Muslims from entering the US until America's security has been assured.