Mexico's government has announced the country's largest-ever seizure of the synthetic opioid drug fentanyl.

President Claudia Sheinbaum told reporters on Wednesday that soldiers found a total of 1,100 kilograms of fentanyl pills in a house and a vehicle in the northwestern state of Sinaloa.

Sheinbaum said the amount totals more than 20 million doses, and stressed that the seizure resulted from a long-term investigation.

Her comments were apparently intended to underline Mexico's antidrug efforts in response to US President-elect Donald Trump's criticism of the country over the cross-border flow of fentanyl into the United States.

Trump says that when he takes office on January 20, he will impose a 25-percent tariff on imports from Mexico and Canada unless they stop illegal immigrants and drugs from coming into the United States through their borders.

Deaths from fentanyl overdose have become a serious social problem in the US.