US law enforcement officials apprehended more than 130,000 people trying to cross the border illegally in May, the highest monthly total on the southern border in 13 years, according to official figures released Wednesday.

Of the 132,887 people detained, 84,542 were people travelling in family units, 11,507 were unaccompanied children, and 36,838 were single adults, according to the U.S. Customs and Border Protection.

The number of apprehensions in May is a 34 percent rise from April's 99,304. A further 11,391 people were turned away in May, registering a light uptick from the previous month.

The influx of migrants has been a constant focus of U.S. President Donald Trump as his administration is pressuring the Mexican government to curb the flow of immigrants, many of whom originated from central American countries, seeking entrance to the United States.

Trump said last week that he would impose a 5-percent tariff on all imported Mexican goods beginning June 10 so as to pressure the country to stop the flow of undocumented migrants crossing the border, and will gradually increase tariffs until the problem is remedied.

In response to the U.S. pressure, Mexican Foreign Minister Marcelo Ebrard is holding talks with U.S. Vice President Mike Pence in Washington Wednesday.