President Donald Trump said Friday that if migrants approaching the U.S. border throw rocks at U.S. military or border patrol personnel like they did with Mexican authorities, they will be arrested, not potentially shot.

Trump was clarifying his previous remarks from the day before and appeared to walk back the suggestion that he would authorize the use of lethal force against a rock thrower.

“[The military] won’t have to fire. What I don’t want is these people throwing rocks .... What they did to the Mexican military is a disgrace. They hit them with rocks. Some were very seriously injured, and they were throwing rocks in their face.”

“They do that with us, they’re going to be arrested, there are going to be problems. I didn’t say shoot. I didn’t say shoot. But they do that with us, they are going to be arrested for a long time,” Trump said Friday.

The comments seemed to de-escalate remarks he made Thursday at a White House press conference where he said any rock thrown by a migrant would be considered the same as if they were wielding a rifle against law enforcement or the military.

“I told them, ‘consider that a rifle,'" Trump said Thursday. “When they throw rocks like they did at the Mexico military and police, I say 'consider it a rifle,” the president said.

Trump’s comments Thursday were widely criticized as an authorization for troops to consider stone-throwing proportional to the use of a firearm, and respond with equal levels of lethal force.

The distinction is critical because the rules of engagement that the U.S. military follows determine precisely what level of force individual service members will use in various situations, including self-defense.

Also, on missions on U.S. soil, where they are serving in a support role to civilian government agencies, the military can not perform law enforcement duties, such as arrests, if the incident occurs outside of federal property such as a military base.

On Friday Trump said border patrol or U.S. Customs and Immigration Enforcement would perform the arrests.

Hours after Trump’s remarks on Thursday, the Nigerian Army cited his comments to justify the recent fatal shooting of rock throwers in Nigeria.

Capitol Hill Bureau Chief Leo Shane contributed to this report.