Washington, Aug 23: US President Donald Trump has threatened to shut down the government, if necessary, to make sure his proposed wall along the Mexican border is approved and funded by lawmakers. The President told supporters at a "Make America Great Again" rally in Phoenix, Arizona, on Tuesday that the opposition Democrats were being "obstructionist", The Hill magazine reported. "Build that wall. Now the obstructionist Democrats would like us not to do it, but believe me if we have to close down our government, we're building that wall," Trump said. Funding for Trump's proposed border wall, a promise that was at the centre of his 2016 presidential bid, is poised to be at the centre of debate when Congress negotiates a new government funding bill. If a new bill is not passed, the government will shut down on October 1. Trump wants Congress to finance his controversial plan to build a "big, beautiful" wall along the US's border with Mexico to keep out illegal immigrants. But Republicans will need the support of Democrats to secure funding for the wall in a government spending bill, which they are unlikely to get, reports said. Democrats are staunchly opposed to funding for the wall, setting up a challenge and tense negotiations over the government's funding. In his speech, Trump said the Democrats were "putting all of America's safety at risk" by opposing the wall. He said immigration officers who worked in the area said it was "vital" to stem the flow of illegal immigrants. The Department of Homeland Security accepted designs for the wall earlier this year. Vendors were instructed that the wall should be at least 18 feet high, have features to prevent climbing over and tunnelling beneath the structure, and to make the designs "aesthetically pleasing" on the US side, the report said.