Mexico has formally asked the United States for evidence behind its claim that US security personnel were fired on from across the Mexican border, saying its own forces found no sign that any shots were fired from Mexican territory. President Claudia Sheinbaum raised the demand at her daily news conference on Monday, days after the allegation prompted a deployment of about 500 US troops to the border.

Sheinbaum said Washington had reported “shots from the Mexican border”, but that Mexico’s National Guard, Army and Navy had detected no gunfire directed from Mexico towards the United States. “We asked for all the evidence because we have no evidence,” she told reporters.

What the US says happened

The dispute centres on an incident in late September in Texas, across the Rio Grande from the Mexican state of Tamaulipas. The US Ambassador to Mexico, Ronald Johnson, wrote on social media that members of the US Coast Guard had been fired upon and that the threat would be “swiftly addressed”.

Johnson added that the US Embassy in Mexico was helping to coordinate with Mexican forces deploying to the border area where the Coast Guardsmen were fired upon. “Together, we intend to patrol both sides of our shared border, protect our communities, and make it more difficult for criminal and terrorist organizations to operate,” he wrote.

According to the US Coast Guard, its personnel were taking part in joint interdiction work near Garceno, Texas, on 26 September when gunfire came from the Mexican side of the river. The Coast Guard said its personnel returned fire, with no injuries and no damage to vessels or equipment reported. The incident remains under investigation.

Troops sent to the border

Some 500 US troops, along with helicopters, drones and anti-drone equipment, have been sent to the border area since the alleged shooting. Mexico has also sent its own deployment to the area, as part of a joint effort the two countries call Operation Mirror, intended to secure the frontier.

Sheinbaum confirmed that the Mexican deployment was designed “to forestall any issues” that may arise. A US State Department spokesman said information about the shooting had been shared with the Mexican government through official channels, but US officials have not publicly identified the shooters or explained how they determined where the gunfire came from.

A wider strain in relations

The disagreement is the latest friction between Sheinbaum and Johnson, a former US Army Green Beret and CIA officer who has served as ambassador since May 2025. The two have repeatedly clashed over border security and national sovereignty, with Sheinbaum accusing the ambassador of overstepping diplomatic norms and Johnson pressing Mexico to cooperate more closely with President Donald Trump’s demands.

Trump has repeatedly said he may carry out military strikes inside Mexico against the drug cartels he says are “running Mexico”, framing them as a threat to US security. Sheinbaum has warned that such an operation would violate Mexico’s sovereignty.

For now, both governments say their joint border operation continues, even as they publicly disagree about what happened on the river in September. Mexico is still waiting for the evidence it has asked Washington to provide.