Mexico has deployed 6,000 members of its National Guard on its border with Guatemala in an attempt to stem the flow of migrants heading to the US.
Mexico’s Foreign Minister Marcelo Ebrard is in Washington trying to stop the US from placing trade tariffs on Mexican goods over illegal migration.
US President Donald Trump has vowed to enact import duties of 5% on Monday if no agreement is reached.
On Wednesday, he said “not nearly enough” progress was being made.
After the latest talks on Thursday, Mr Ebrard said he was “an optimistic man.”
He said forces would be stationed on Mexico’s southern border with Guatemala to prevent migrants entering the country.
US Customs and Border Protection announced this week that migrant arrests had surged in May to the highest level in more than a decade.
Border Patrol apprehended 132,887 migrants attempting to enter the US from Mexico in May, marking a 33% increase from the month before.
It said 84,542 were families and 11,507 unaccompanied children.
The arrests were the highest monthly total since Mr Trump took office.
Another 11,391 migrants were deemed “inadmissible” and turned away after arriving at US ports of entry, bringing the overall figure to 144,278.
“We are in a full-blown emergency, and I cannot say this stronger, the system is broken,” said acting CBP Commissioner John Sanders.
Official figures show illegal border crossings have been in decline since 2000.
In 2000, 1.6 million people were apprehended trying to cross the border illegally – that number was just under 400,000 in 2018.
In 2017, Mr Trump’s first year in office, the figures were the lowest they had been since 1971.
The decline was in large part due to a dip in the number of people coming from Mexico.
In the past two years, however, the number of arrests has been rising again, especially in recent months.