cartels@ (Updates with Mexican president)
MEXICO CITY, Dec 1 (Reuters) - Clashes between police and suspected cartel gunmen in a northern Mexican town killed 21 people this weekend, authorities said, adding fuel to bilateral tensions sparked by U.S. President Donald Trump's vow to designate the drug gangs as terrorists.
Mexican President Andres Manuel Lopez Obrador, who is pushing a less confrontational approach to subduing the cartels, repeated on Sunday that he would not accept any intervention from abroad, while doubling down on his strategy of containment.
The government of the northern state of Coahuila said local security forces killed seven gunmen early on Sunday, adding to 10 others who were shot dead during exchanges in and around the small town of Villa Union not far from the Texas border.
Four police were also killed and six wounded in the shootouts, which stunned residents of the town around midday on Saturday, sparking alarm on social media and fresh criticism of the government's approach to handling the powerful gangs.
Riding into town in a convoy of heavily armed pickups, gunmen sprayed the offices of the mayor of Villa Union with bullets and fought police for more than an hour.
Heavy gunfire echoed through the town on videos broadcast on social media and local television.
Most of the downed gunmen, who were suspected members of the Cartel of the Northeast from Tamaulipas state to the east, were killed by state police in pursuit of the raiding party after it fled the town, Coahuila's government said.
The events in Villa Union add to a series of recent security lapses that have raised questions about Lopez Obrador's policy.
During a speech in front of tens of thousands of supporters on the first anniversary of his presidency, Lopez Obrador again said Mexico would handle its security problems, in a nod to Trump's comments earlier in the week.
"We won't accept any kind of intervention, we're a sovereign, free country," the 66-year-old veteran leftist said in Mexico City's Zocalo central square.
Trump's remarks have stirred concerns in Mexico that Washington could try to take unilateral action to crush the drug cartels. U.S. Attorney General William Barr is due to visit the country next week to discuss cooperation on security.
U.S. and Mexican criticism has focused on the Nov. 4 massacre of nine women and children of U.S.-Mexican origin from Mormon communities in northern Mexico, and the armed forces' release of a captured son of drug lord Joaquin "El Chapo" Guzman under pressure from cartel gunmen in the city of Culiacan.
Critics accuse Lopez Obrador of caving in to the gangs, but he defended the Culiacan episode during the speech, saying the release of Ovidio Guzman had prevented unnecessary bloodshed.
"Our adversaries can say we showed weakness, but nothing is more important than people's lives," he said.
Homicides reached record levels in Mexico last year and are on track to surpass that total this year.
(Reporting by Dave Graham and Noe Torres Editing by Lisa Shumaker and Alistair Bell)