For months, U.S. and Mexican officials had been watching “El Menchito.”

The suspect — allegedly a top figure in the Jalisco New Generation cartel — had been arrested by Mexico’s army in 2015 on drug-trafficking charges. But he had dodged extradition to the United States through legal maneuvers.

On Thursday afternoon, though, a judge dismissed his lawyers’ latest objections. Mexican officials hustled the suspect — a baby-faced man in a khaki jumpsuit — onto a helicopter and whisked him to an airstrip in northern Mexico, according to a U.S. official. Within the hour, the alleged trafficker was on an airplane bound for Dulles International Airport.

The handover was part of a little-noticed surge of extraditions that have occurred since early December, when Attorney General William P. Barr visited Mexico to express concern over the government’s response to soaring violence.

El Menchito — Rubén Oseguera González — is perhaps the best-known suspect extradited so far. But around 40 other alleged organized-crime figures have been sent to the United States since Barr’s Dec. 5 trip, officials say. They include Ismael Zambada Imperial, the son of another major trafficker, as well as José María Guizar Valencia, a leader of the hyperviolent Zetas organization.

“The numbers are up dramatically,” said the U.S. official, who spoke on the condition of anonymity because he was not authorized to comment.

Oseguera, 30, was arraigned Friday in federal court in the District on counts of distributing cocaine and methamphetamine and using a firearm to facilitate drug trafficking. He pleaded not guilty on all counts, which carry a minimum sentence of 15 years in prison.

Federal prosecutor Brett Reynolds said Oseguera, who wore a tan jumpsuit and spoke only to answer a judge’s questions, was a serious flight risk and asked that he be held until trial. A judge set a detention hearing for Wednesday.

Mexican officials said 30 Mexicans have been extradited to the United States so far in 2020. Alfonso Durazo, Mexico’s secretary of public security, confirmed Friday morning Oseguera had been extradited in a “joint operation” with U.S. authorities.

Since taking office in December 2018, President Andrés Manuel López Obrador has pledged to combat organized crime with social programs and a new National Guard. But U.S. officials became increasingly worried last year as Mexico’s efforts appeared to flag.

In all of 2019, 58 Mexicans were extradited to face U.S. charges, down from 69 the previous year, according to Foreign Ministry documents obtained by The Washington Post under Mexico’s Freedom-of-Information law.

The army seized 62 percent less heroin in the first 11 months of 2019 than in the same period a year earlier, and eradicated less than half as much poppy. Meanwhile, homicides ticked up nearly 3 percent to 35,588, reaching historic levels.

What really galvanized U.S. attention were two events. In October, Sinaloa cartel gunmen stormed the city of Culiacán, forcing Mexican authorities to release the son of Joaquin “El Chapo” Guzman shortly after his capture. Weeks later, assailants massacred three women and six children — all dual U.S.-Mexican nationals — in the northern state of Sonora.

While Mexico’s government has played down the spate of extraditions in public, officials say privately they have developed a close working relationship with the U.S. Justice Department and are deploying lawyers to fight efforts by suspects’ attorneys to bog down extradition cases with frivolous petitions.

Barr has also said little publicly about his trips to Mexico in December and on Jan. 17. But Trump’s threat in November to designate Mexican cartels as terrorist groups appears to have given him considerable leverage. Trump backed off that plan after Mexican officials protested that it would damage their nation’s economy and international image.

Oseguera was one of the most important figures on the U.S. list of alleged traffickers tied up in extradition proceedings. He is the son of Nemesio Ruben Oseguera Cervantes — “El Mencho” — leader of the Jalisco cartel, viewed as one of Mexico’s most powerful drug organizations. The Justice Department has described the younger Oseguera as the second-in-command of the cartel.

For decades, U.S. officials have pushed Mexico to send alleged traffickers to face American prosecution, given the weakness and corruption of the Mexican judicial system. That weakness was on display last month, when three accused Sinaloa Cartel operatives wanted by the U.S. government broke out of the Reclusorio Sur prison in Mexico City. They fled in an official vehicle with a chauffeur, according to Mexican media reports. Several government employees were detained on suspicion of complicity.

Mexico has extradited some major drug figures, notably Joaquin ‘El Chapo’ Guzman, a legendary figure who headed the Sinaloa cartel. He was convicted in U.S. federal court a year ago on drug, weapons and other charges and sentenced to life in prison.

But sometimes Mexico has been reluctant to transfer suspects to U.S. custody — either out of a sense of nationalism or, perhaps, fear of what secrets the traffickers may reveal about official corruption.

“El Menchito” has insisted he is not guilty, and is not even the son of the renowned trafficker. “In these past five years, I’ve demonstrated my innocence, having been absolved in every single case against me,” he said in a letter published in December by the news magazine Proceso.

Jouvenal reported from Washington.