MEXICO CITY (Reuters) - Clashes sparked by suspected cartel gunmen in a northern Mexican town killed 20 people this weekend, authorities said, putting more pressure on Mexico’s president to curb gang violence after the United States vowed to label the gangs terrorists.

President Andres Manuel Lopez Obrador, mindful of efforts by U.S. President Donald Trump to designate Mexican drug gangs as terrorist groups, repeated on Sunday that he would not accept any intervention from abroad, while doubling down on his strategy of trying to contain the cartels.

But the killings clouded celebrations marking Lopez Obrador’s first year in office, which were buffeted by a march in Mexico City by thousands of people protesting the violence.

The government of the northern state of Coahuila said local security forces killed 14 gunmen on Saturday and Sunday, after a major gunfight broke out in the small town of Villa Union near the Texas border. Earlier, the state government had said police had shot dead 17 cartel members.

Four police were also killed in the shootouts, which broke out around midday on Saturday, sparking fresh criticism of the government’s approach to handling the powerful gangs.

The bodies of two unarmed civilians apparently murdered by the gunmen were also recovered, the government said.

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 1 1/2 hours as gunfire echoed through the streets.

More than 60 gunmen took part in the fight and 17 of their vehicles were seized, Coahuila’s government said.

A number of the gunmen, who were suspected members of the Cartel of the Northeast from Tamaulipas state, were killed by state police in pursuit of the raiding party after it fled the town, authorities 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 his first anniversary as president, Lopez Obrador again said Mexico would handle its security problems, after Trump’s comments.

“We won’t accept any kind of intervention, we’re a sovereign, free country,” the 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.

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Criticism at home and abroad has focused on the Nov. 4 massacre by suspected cartel gunmen 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 threats from his gang in the city of Culiacan.

Critics accuse Lopez Obrador of caving in to the cartels, but he defended the release of Ovidio Guzman, saying it had prevented unnecessary bloodshed.

“Our adversaries can say we showed weakness, but nothing is more important than people’s lives,” he said.

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The protest march united opposition politicians with grieving members of the U.S.-Mexican LeBaron family, who lost loved ones in the killings in the state of Sonora.

“We’re not against the president, we’re against the security policies that have been used until now, because they haven’t worked,” said Julian LeBaron, a relative of the victims.

Overnight, law enforcement agents captured several people suspected of involvement in those murders, the attorney general’s office of Sonora said.

Homicides reached record levels in Mexico last year and are on track to surpass that total this year.

Lopez Obrador has also presided over a slowdown in the economy, which has stagnated in 2019.

Yet while there has been some erosion of support for him, most recent opinion polls show he remains popular.