Washington - US President Donald Trump on Thursday told Mexico's president to cancel an upcoming visit to Washington if he is unwilling to foot the bill for a border wall.Escalating a cross border war of words, Trump took to Twitter to publicly upbraid Enrique Pena Nieto."If Mexico is unwilling to pay for the badly needed wall, then it would be better to cancel the upcoming meeting."Talks have been scheduled to take place at the White House next week. On Wednesday, the mercurial US leader ordered officials to begin to "plan, design and construct a physical wall" along the 3 200km US-Mexico border.Stemming immigration was a central plank of Trump's election campaign, although there are still serious doubts about how the project will be funded.Trump's decision put Pena Nieto under fierce domestic pressure to hit back, and hit back he did in a video message to the nation late Wednesday.Hardball approach"I regret and condemn the decision of the United States to continue construction of a wall that, for years, has divided us instead of uniting us," Pena Nieto said."I have said it time and again: Mexico will not pay for any wall," he added.By Thursday morning, Trump' had issued his bareknuckle public response, which may shock diplomats but is in keeping with the mogul's hardball approach to negotiations.Trump also took to Twitter to gripe about the trade gap between Mexico and the United States."The US has a 60 billion dollar trade deficit with Mexico. It has been a one-sided deal from the beginning of NAFTA with massive numbers of jobs and companies lost," he said.Trump has said he will seek to renegotiate the 23-year-old North American Free Trade Agreement.