The office of New York City Mayor Bill de Blasio on Wednesday disputed allegations from U.S. Border Patrol that he illegally crossed into the U.S. from Mexico away from a formal point of entry, and said his back-and-forth between the U.S. and Mexico was approved by a Border Patrol official.

The most senior Border Patrol official in the El Paso Sector, Chief Patrol Agent Aaron Hull, wrote a letter to New York Police Department Commissioner James O’Neill on June 25 that said de Blasio had chosen to enter Mexico without inspection, then illegally entered back into the U.S. on foot in an attempt to see a border detention facility.