MEXICO, March 7 (Xinhua) -- Mexico is "gravely concerned" over a U.S. proposal to separate undocumented migrant families crossing the U.S.-Mexico border, Foreign Minister Luis Videgaray said on Tuesday.

"We immediately informed the Department of Homeland Security of our grave concern ... due to the irreversible damage that a situation like this can have on numerous Mexican families," Videgaray told reporters following a meeting with lawmakers.

"Mexico's position was expressed clearly and in a timely manner," and "we hope the opinion of the Mexican government has an influence on the decision the U.S. government finally takes," said Videgaray.

Last week, the U.S. department said it was mulling a policy to separate families as a way to discourage the arrival of undocumented migrants. The scheme would place children in protective custody while their mothers are sent to detention centers to await deportation.

Up to now, families have been kept together and usually released before being deported.