Mexican President Enrique Pena Nieto late Wednesday slammed his US counterpart Donald Trump's decision to order a barrier to be built along the length of the Mexican border. "I regret and condemn the decision of the US government to continue with the building of a border which for years has divided us more than it has united us," he said in a televised address. "I've said it time and time again: Mexico will not pay for the wall," he added, despite Trump's continued insistence that Mexico would fund the project. "Mexico gives and demands the respect it is due as a sovereign nation," Pena Nieto said. Many Mexicans had called on their president to cancel a planned visit to the US next week to protest the US move, but Pena Nieto made no mention of the trip in his address. They regarded the timing of the signing of the order as an insult to Mexico, coming as it did during a visit to Washington by Mexican Foreign Minister Luis Videgaray and Economy Secretary Ildefonso Guajardo. "Mexico offers its friendship to the people of the United States and its willingness to reach agreements with their government. Agreements which will benefit Mexico and Mexicans," Pena Nieto said. Trump's order called for the "immediate construction of a physical wall on the southern border," and for the detention of illegal immigrants and the quick removal of those whose claims to stay in the US had been rejected. "A nation without borders is not a nation," Trump told border patrol agents and other staff at the Department of Homeland Security where the signing took place. Trump, who said the wall would save thousands of lives, millions of jobs and billions of dollars, called the situation along the 3,200-kilometre border a "crisis" and declared "beginning today the US gets back its borders." There are an estimated 11 million illegal immigrants in the United States, primarily from Mexico and the rest of Latin America. In an interview with ABC News, Trump said construction on the wall would begin in "months" and said that US tax dollars would be used to begin the construction but that Mexico would ultimately reimburse Washington. He also signed a second executive order to address law enforcement surrounding unauthorized immigrants, including stripping federal grant money from "sanctuary cities," where leaders have refused to hand over illegal immigrants for deportation. The erection of a "big, beautiful wall" along the Mexican border had been one of Trump's key campaign pledges. However, its construction will be a vast task, spanning four US states and rough terrain of deserts and mountains. A fence and other barriers already exist along portions of the border. Immigrant groups denounced Trump's order. "President Trump's executive actions go against the principles and values that our country was founded on and will only tear families apart," Cesar Blanco, of the Latino Victory Project said.