Mexico has urged the US to designate as an act of terrorism the recent mass shooting that killed 22 people in an El Paso Walmart shop. A four-page statement believed to have been written by accused shooter Patrick Crusius and posted on 8chan, an online message board often used by extremists, called the El Paso attack "a response to the Hispanic invasion of Texas". Mexico has been investigating the tragedy as a terrorist act. On Wednesday it reasserted that the shooting was an act of terrorism against Mexicans and urged the US to ensure it was designated as such. After meetings on Tuesday between US and Mexican government officials, Mexican Foreign Minister Marcelo Ebrard said steps needed to be taken to prevent future killings. "It's very important to persevere; to specify, clarify and demand that measures are taken so that this is not repeated," Mr Ebrard said. "And the first measure is to classify it for what it is, an act of terrorism that seeks to take Mexican lives." An El Paso police affidavit released on Friday said Crusius told police while surrendering that he had been targeting "Mexicans". "There will be those who say, 'this isn't terrorism, it's just one person'," Mr Ebrard said, alongside Mexican President Andres Manuel Lopez Obrador. "Well, it needs to be said that the man who carried out this despicable, abominable and appalling act is part of a network, but he also uploaded a manifesto to the network. "What he says is terrible but it's not that he's mad. He is in possession of his faculties." The Mexican government has said it may also request that the perpetrator be extradited to Mexico for trial, which Mr Lopez Obrador repeated at a public event later on Wednesday. "We're going to ask for this person be judged here, too," he said. "We're going to ask for his extradition and the full weight of the law will be felt." Mr Lopez Obrador said Mexico did not allow the death penalty but could impose severe sentences. "We don't want this to happen again," he said. "We don't want these hate crimes." The attack caused widespread shock in Mexico at a time of persistent diplomatic tension between the US administration and the Mexican government over trade and immigration. Mexico's government last week pressed the US to co-operate in helping to identify white supremacists who are a threat to its citizens.