A shootout in Mexico near the US border between suspected drug traffickers and police left at least 21 dead, including four officers, officials said Sunday.

The confrontation started shortly before noon on Saturday in the northern state of Coahuila when officers detected several vehicles and heavily armed passengers touring the small community of Villa Union, 60 kilometers (40 miles) from the border.

Shooting continued into early Sunday, the Coahuila state government said, adding that four of those killed were police, 14 were suspected criminals and another three bodies were unidentified.

Local authorities said three trucks were seized in the operation, as well as several high-caliber weapons and an unspecified load of ammunition.

Video footage showed the bullet-ridden mayor’s office.

The shootout comes after Mexico’s leader Andres Manuel Lopez Obrador warned that he would not allow the US to conduct cross-border armed operations against drug cartels in the country.

US President Donald Trump has been talking tough on the cartels since one was allegedly responsible for the massacre of nine women and children from a US-Mexican Mormon community in northern Mexico on November 4.

Trump said last week he plans to designate Mexican drug gangs as terrorist organizations.