US authorities have arrested more people in the past three months linked to detention centres in Mexico, the US government said on Friday, a day after the government announced the first arrests in an investigation into the deaths of migrants.
US Attorney General Eric Holder said the cases were related to illegal border crossings, but did not elaborate.
The crackdown on migrants comes as Mexican President Enrique Pena Nieto is trying to improve relations with Washington.
He is trying for better ties with the United States after a series of deadly incidents at US-Mexico border crossings.
On Wednesday, he said he would call on Mr Pena to renegotiate the $US50bn (£33bn) trade deal he signed with the US in 2018.