UPDATE 1-Trump rejects Mexican efforts in face of fresh migrant caravan

U.S. President Donald Trump on Wednesday again threatened to close part of the southern border and send more "armed soldiers" to defend it if Mexico did not block a new caravan of migrants traveling toward the United States. "A very big Caravan of over 20,000 people started up through Mexico," Trump wrote on Twitter. "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."

Trump also said, without offering details, Mexican soldiers recently had "pulled guns" on U.S. troops in what he suggested was "a diversionary tactic for drug smugglers." "Better not happen again! We are now sending ARMED SOLDIERS to the Border. Mexico is not doing nearly enough in apprehending & returning!" Trump tweeted.

It was not clear what Trump meant by "armed soldiers" since they typically carry weapons. It also was unclear what specific caravan Trump was alluding to. There have been no reports of gunfire involving U.S. and Mexican troops at the border.

A Mexican government official said a group of Mexican soldiers on April 13 interrogated two U.S. soldiers who were traveling near the Texas border. Although the Mexican troops believed the U.S. soldiers were south of the border and therefore in Mexico, the soldiers were in U.S. territory despite being south of a border fence. After a brief discussion, the Mexicans troops left the area, the Mexican official said.

Newsweek magazine, citing the military report on the incident, said it took place near Clint, Texas, about 30 miles (48 km) southeast of El Paso. It said the U.S. soldiers were in an unmarked car and briefly held at gunpoint by the Mexicans, who took one U.S. soldier's gun and put it in the car. Asked about Trump's tweet at a news conference, Mexican President Andres Manuel Lopez Obrador said his administration would investigate the incident Trump mentioned.

"But we're not going to fight with the U.S. government," he said. "We are not going to allow ourselves to fall into any provocations." Trump, who has made a tough stance on immigration a cornerstone of his presidency, has called the situation at the southern border a national emergency.

Officials arrested or denied entry to more than 100,000 people along the Mexican border in March, more than twice as many as during the same period last year, according to U.S. Customs and Border Protection. In response, the Trump administration has moved border agents to handle an influx of migrants. Military personnel were sent in late last year and there currently are about 5,000 active-duty and National Guard troops currently at the border, where they have been operating mobile surveillance cameras and stringing concertina wire.

In March, Trump threatened to close the border if the Mexican government did not immediately stem illegal migration, although later, he praised Mexico for efforts to stop people from crossing illegally into the United States. Mexico has returned 15,000 migrants in the past 30 days, a senior government official said on Tuesday, pointing to an uptick in deportations in the face of pressure from U.S. Trump to stem the flow of people north. (Reporting by Makini Brice; Additional reporting by Idrees Ali in Washington and Adriana Barrera, David Alire Garcia and Dave Graham in Mexico City; Editing by Susan Heavey and Bill Trott)