MEXICO CITY — Amid another round of violence that claimed more than 20 lives, a top U.S. drug official Friday sounded an alarm over the number of killings and kidnappings that spill into the southern United States from Mexico.

Mexican authorities and other reports from around the country said at least 23 people were killed late Thursday and Friday, including three police officers who died in a gun battle in the state of Jalisco. In the border state of Chihuahua, six men were lined up against a wall at a gymnasium and shot to death.

U.S. drug czar John Walters, in Mexico City to reassure officials that American aid to fight drug gangs is in the pipeline, said traffickers resort to "fear and horror" in their campaign to take over government institutions but will ultimately fail. "It's not just about drugs," Walters told a news conference. "It's about kidnapping and murder. It's about extortion ... and suborning government officials."

Although Mexican society suffers the brunt of the violence, Walters said, drug gangs and their hitmen cross the border into the U.S. with relative ease to settle scores and carry out slayings there.

"These groups do not respect the border," said Walters, who is head of the White House Office of National Drug Control Policy.

More than 3,000 people have been killed in Mexico in warfare that has raged since President Felipe Calderón deployed 40,000 army troops to crack down on the most powerful drug networks.

Despite the intensifying bloodshed, Walters praised Calderón's efforts.

Ultimately, he said, the druglords will face a stark choice: "They surrender, or they die." Walters reiterated his government's intention to begin releasing parts of a $400 million package of aid and training under the so-called Mérida Initiative approved by the U.S. Congress earlier this year. In addition to countering the violence, the package targets money laundering and gun smuggling, illicit businesses that sustain the largest cartels.