Mexican security forces have impounded more than a ton of fentanyl pills in what officials have called the biggest seizure of the synthetic opioid in the country’s history.

Soldiers and marines found the fentanyl at two properties in the northern state of Sinaloa, late on Tuesday – exactly a week after Donald Trump threatened to impose 25% tariffs on products from Canada and Mexico unless the two neighbouring countries cracked down on the flow of immigrants and drugs across their borders with the US.

Mexican authorities also said they had apprehended more than 5,200 migrants across the country on Tuesday, signaling a further ramp-up in enforcement aimed at stopping people from reaching the US border.

Fentanyl seizures in Mexico have dropped this year, and experts said the timing of the announcement of the drug raids may not be a coincidence.

“It is clear that the Mexican government has been managing the timing of fentanyl seizures,” said security analyst David Saucedo. “But under the pressure by Donald Trump, it appears President Claudia Sheinbaum’s administration is willing to increase the capture of drug traffickers and drug seizures that Washington is demanding.”

Saucedo said it’s clear the Mexican government “doesn’t see fentanyl as one of its own problems, and fighting it isn’t its priority”. He added there would only be big busts “when there is pressure from Washington”.

Mexico’s top security official said the raids had been launched after soldiers and marines late Tuesday spotted two men carrying guns, who ran into two houses when security forces gave chase.

In one house, soldiers found about 660lbs (300kg) of fentanyl, and in the other, a truck packed with about 1,750lbs (800kg) of the drug, mostly in pill form.

“In Sinaloa, we achieved the biggest seizure in history of fentanyl,” Omar Garcia Harfuch, the public safety secretary, wrote on his social media accounts. Several guns were also seized and two men were arrested.

Sheinbaum said Wednesday that “this is an investigation that had been going on for some time, and yesterday it bore fruit”.

That claim appeared to contrast with the seemingly random nature of the bust as described by Harfuch.

In the past, Mexican security forces have sometimes used the story of following armed men running into houses as a pretext to enter homes without search warrants.

The latest haul was also striking because fentanyl seizures in Mexico had fallen dramatically in the first half of the year.

Figures for the first half of 2024 show that Mexican federal forces seized only 286lbs (130kg) of fentanyl nationwide between January and June, down 94% from the 5,135lbs (2,329kg) seized in 2023.

The synthetic opioid has been blamed for about 70,000 overdose deaths annually in the United States, and US officials have tried to step up efforts to seize it as it comes over the border, often in the form of pills made in Mexico from precursor chemicals largely imported from China.

“It’s a very, very big seizure,” Saucedo said. “But if they don’t dismantle the labs, this kind of production will continue.”