The escalating feud between Republican presidential candidate Donald Trump and Mexican President Enrique Peña Nieto has officially spilled over onto Twitter. Despite the surprisingly diplomatic nature of their meeting and press conference in Mexico City on Wednesday, the two men remain in stark disagreement about who will foot the bill for Trump’s desired border wall between the two countries. When asked by reporters if they discussed payment for the wall in their closed-door meeting, Trump said no. President Peña Nieto later claimed that he began the meeting by telling Trump Mexico would never pay for it.

During his big immigration speech that followed in Phoenix, Arizona, Trump declared to cheers from his supporters that “Mexico will pay for the wall. One hundred percent.” He then added, “They don’t know it yet, but they’re going to pay for it.” Trump tweeted the same message early Thursday morning, which has now prompted a direct response from Peña Nieto: “I repeat what I said personally, Mr. Trump: Mexico would never pay for a wall.”