U.S. President Donald Trump said here late Monday that the country needs to build a wall fast to protect its borders from Central American migrants.

During the "Make America Great Again" rally at Toyota center in downtown Houston, the fourth largest city in the United States, Trump told a crowd of nearly 180,000 that the caravan of migrants heading towards the United States is "assault on our country" and that "we need a wall built fast."

Earlier on the day, Trump said Washington will begin cutting off or reducing aid to Guatemala, Honduras and El Salvador, citing migrant caravans heading to the U.S. border.

Trump's Houston rally is his latest campaign appearance leading to the mid-term elections set on Nov. 6. He will go to Wisconsin, North Carolina and Illinois to galvanize more supporter for the Republicans.

Over the weekend, thousands of migrants, mostly from Honduras, have swarmed into Mexico after passing the Guatemalan border. Media reported that Mexican police watched the procession with vigilance but did not disturb the migrants' journey.

Official data showed that the Trump administration has sharply slashed aid to the three countries in Central America, projecting some 40-percent plunge in aid in the 2019 financial year compared with that of 2016.