WASHINGTON – President Donald Trump said on Wednesday the US is sending armed soldiers to the southern border after Mexican soldiers recently "pulled guns" on US troops, escalating his war of words with Mexico on immigration.

Trump was apparently referring to an April 13 incident in which Mexican troops reportedly questioned and pointed their weapons at two US troops conducting surveillance on the border.

"Mexico's Soldiers recently pulled guns on our National Guard Soldiers, probably as a diversionary tactic for drug smugglers on the Border. Better not happen again!" he tweeted.

"We are now sending ARMED SOLDIERS to the Border. Mexico is not doing nearly enough in apprehending & returning!"

Mexico's President Andres Manuel Lopez Obrador said his government would analyse the incident, take into account Trump's comments, and act "in keeping with law within the framework of our sovereignty."

"We are not going to fall for any provocation," he told reporters in Mexico City.

"The most important thing is to tell (Trump) we are not going to fight with the government of the United States. The most important thing is to say we want a relationship of mutual respect and cooperation for the sake of development."

It was unclear if Trump was signalling a new deployment or any change in the way US troops on the border are armed or in the rules under which they operate.

A Pentagon official said some of the 2,900 active duty and 2,000 National Guard troops deployed at the border have always been armed "for force protection only."

"We are always reviewing our policies," the official added, speaking on condition of anonymity.

Unmarked border area

US Northern Command said the two US soldiers involved in the April 13 incident were in an unmarked vehicle conducting "border support operations" on the American side of the border when they were approached by five to six Mexican military personnel.

The incident occurred north of the Rio Grande in Texas, but in an unmarked area south of the border fence.

An inquiry "revealed that the Mexican military members believed that the US Army soldiers were south of the border. However, the US soldiers were appropriately in US territory," NORTHCOM said.

Defense officials told CNN the Mexican soldiers pointed their weapons at the US troops, removed a soldier's sidearm and returned it to their unmarked vehicle.

The command's statement said only that the Mexican soldiers departed the area "after a brief discussion between the soldiers from the two nations."

"Throughout the incident, the US soldiers followed all established procedures and protocols," it added.

The Mexican Foreign Ministry confirmed the incident but downplayed it, saying the Americans were in fact in an unmarked car south of the fence but north of the border in a spot that is not clearly marked either as Mexico or the US.

"This kind of incident is common, as it is a matter of verifying an ordinary patrol, without consequences for either government, which communicate permanently and fluidly." the ministry said in a statement.

Trump: big new caravan

Trump, who has made the immigration the core of his message to his conservative base, also said on Twitter that "a very big Caravan of over 20,000 people" is making its way through Mexico toward the US.

"It has been reduced in size by Mexico but is still coming. Mexico must apprehend the remainder or we will be forced to close that section of the Border & call up the Military. The Coyotes & Cartels have weapons!," Trump wrote.

Mexico's president wants to curb the flow of migrants through his country toward the US, mainly to ensure their safety as the trip is very dangerous.

These travelers, often with children and even babies, risk violence and kidnapping from crime gangs as well as physical exhaustion.

Mexican authorities recently have proposed replacing existing humanitarian visas that allow migrants entering Mexico to travel freely around the country, with one that restricts their movements to its southern states.

Migrants who move north toward the US under the proposed new visa would risk expulsion.

In yet another tweet, Trump praised what he said was great work being done by US border patrol and law enforcement officials.

"So far this year they have APPREHENDED 418,000 plus illegal immigrants, way up from last year," Trump wrote.

Since October of last year, thousands of Central American migrants grouped into so-called caravans have traveled through Mexico in the hope of reaching the United States and a better life. – AFP