Customs and Border Protection officials said most of the migrants were families from Guatemala, Honduras and El Salvador, and the total included some 57,718 children.

 

The total number of migrants detained in the past month was nearly triple that of a year ago, underscoring the surge that has overwhelmed border agents and sparked a deep crisis in US relations with Mexico, which Washington has accused of abetting the immigrant flow.

 

"We are in a full-blown emergency. The system is broken," said CBP Acting Commissioner John Sanders.

 

The numbers were released hours before top Mexican officials were to meet with Vice President Mike Pence over President Donald Trump's threat to impose steep tariffs on Mexican goods starting Monday if it doesn't do something to keep the migrants from reaching the US frontier.

 

Sanders said there had been no let-up in the numbers of border crossers in the first days of June, and that the Border Patrol now has nearly 19,000 migrants in custody.

 

Officials said that the pace of arrivals of undocumented migrants -- 677,000 in the first eight months of the fiscal year -- is the highest since 2006, when single men from Mexico were the main migrants, compared to families from Central America today.

 

Sanders said more were arriving in large groups, including one single group of 1,036 which arrived in El Paso, Texas on May 29, the day before Trump announced his tariff threat.

 

Underlining the extent of the crisis, officials said that other nationalities from around the world are joining the trek from Central America to the southern US border.

 

That included a single group of 117 people from sub-Saharan Africa, including Angolans and Cameroonians, detained at Del Rio, Texas last week.