The president of Mexico says that the 15,000 troops his government has deployed along the US border have not been told to detain migrants attempting to cross north, following reports that those forces had forcibly detained two women and a young girl near the Rio Grande river.The comments from Andrés Manuel López Obrador come in direct conflict with comments from his own defence minister, and as Mexico faces pressure from Donald Trump to help slow the flow of migrants into the US."No such order has been issued, and we are going to review that case, so that it doesn't happen again, because that's not our job," Mr Obrador said during a press conference on Tuesday, according to Agence France-Presse.The detention of the two women and young girl was first made public by that news agency, which published a photo of heavily armed National Guardsmen detaining the trio."Those are not the instructions they have. They are not there to do that job. That is the work of the migration authorities, not the army," Mr Obrador said of the incident. "We are going to deal with this matter so that no abuses are committed."Luis Cresencio Sandoval, the defence minister, had initially responded to that image by saying that Mexican forces were detaining migrants to stop them from going to the US."Yes," he said. "Given that [undocumented] migration is not a crime but rather an administrative violation, we simply detain them and turn them over" to immigration authorities.The detentions come as Mexico has attempted to work with the Trump administration on the migrant crisis, which has been fuelled in part by unrest and violence in Central America.Mr Trump, earlier this month, claimed that the country had agreed to help the US after he threatened to hit Mexico with tariffs if they did not cooperate.Mexico has deployed some 15,000 troops to its northern border, a break from traditional policy. Their official role is to help with containment operations in the area.