President Trump declared, "We are now sending ARMED SOLDIERS to the Border," and accused Mexican soldiers of pulling guns on National Guard soldiers "probably as a diversionary tactic."

"Better not happen again!" the president tweeted Wednesday morning. "We are now sending ARMED SOLDIERS to the Border. Mexico is not doing nearly enough in apprehending & returning!"

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! We are now sending ARMED SOLDIERS to the Border. Mexico is not doing nearly enough in apprehending & returning! — Donald J. Trump (@realDonaldTrump) April 24, 2019

It was unclear what incident Mr. Trump was referring to when he said Mexican soldiers "pulled guns." But Newsweek reported last week, citing an serious incident report, that members of the Mexican military briefly held two U.S. Army soldiers at gunpoint earlier this month, believing the soldiers had crossed into Mexican territory.

Get Breaking News Delivered to Your Inbox

Mr. Trump has already sent thousands of troops to the border as he tries to stem illegal crossings. However, U.S. military members are prevented from using force to prevent border crossings.

"A very big Caravan of over 20,000 people started up through Mexico," the president also tweeted Wednesday. "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!"

U.S. Northern Command explained the incident, which appears to have been a misunderstanding about where the unmarked border was, in a statement:

"On April 13, 2019, at approximately 2 p.m. CDT, five to six Mexican military personnel questioned two U.S. Army soldiers who were conducting border support operations in an unmarked CBP vehicle near the southwest border in the vicinity of Clint, Texas. An inquiry by CBP and DOD revealed that the Mexican military members believed that the U.S. Army soldiers were south of the border. However, the U.S. soldiers were appropriately in U.S. territory. Though they were south of the border fence, U.S. soldiers remained in U.S. territory, north of the actual border. After a brief discussion between the soldiers from the two nations, the Mexican military members departed the area. The U.S. soldiers immediately contacted CBP, who responded quickly. Throughout the incident, the U.S. soldiers followed all established procedures and protocols. An inquiry into the incident is ongoing."

The Department of Homeland Security, which oversees Immigration and Customs Enforcement (ICE) and Customs and Border Protection (CBP), has seen a massive shift in leadership in the last month. Former Secretary of Homeland Security Kirstjen Nielsen and other top officials departed in the same week. Top Trump adviser Stephen Miller, a well-known immigration hardliner, has orchestrated some of the changes in immigration strategy behind the scenes. But the president, asked if Miller will be the new DHS head, said only one person is in charge of immigration — him.

"Stephen is an excellent guy. He is a wonderful person. People don't know him. He has been with me from the beginning. He is a brilliant man," Mr. Trump said earlier this month en route to Texas.

"Frankly, there is only one person that is running it. You know who that is? It's me," the president said, pointing to himself.