Investigators in Spain and Argentina have remained tight-lipped about the inquiry, but questions have swirled around the possible involvement of Argentine military officials and politicians who flew on Medical Jet, and deeper connections to Colombian and Mexican drug cartels.

Last week, the Argentine Air Force dismissed Commodore Jorge Ayerdi, the head of the Morón air base, where the Challenger 604 plane took off on Jan. 1, Argentina’s state news agency reported.

Arturo Puricelli, Argentina’s defense minister, has expressed concern about the possible involvement of the air force, saying Wednesday in a radio interview that he would push for an investigation. “There is great indignation about the case within the air force,” Mr. Puricelli said.

The Argentine judge Alejandro Catania is investigating 18 air force officials for possible involvement in the drug shipment, the Argentine news media reported. He declined to comment on the case.

The seized drug cargo was only the most recent of dozens of cocaine shipments to Spain originating in Argentina since 2006, experts on organized crime in Argentina and Spain said.

“Argentina has become a producer and exporter of cocaine over the past five years, and Europe is looking to Argentina for cocaine,” said Claudio Izaguirre, president of the Argentine Anti-Drugs Association, a nongovernmental group in Buenos Aires.

Mr. Izaguirre said that six drug cartels had set up shop in Argentina in the past five years, two from Colombia and four from Mexico.

Argentina has an expansive border with Bolivia and Paraguay, two large drug producers with weak border controls, including scant radar coverage over Argentine airspace, Argentine officials have said. Mr. Izaguirre said Mrs. Kirchner’s government had yet to wake up to the growing drug-trafficking problem, which he said was “getting more and more complicated.”

Spanish interdiction efforts in the past decade point to the increased use of the Southern Cone, especially Argentina, to smuggle drugs into Europe. A joint operation last November that included Brazilian authorities broke apart a trans-Atlantic shipping route to Spain and led to the arrests of 65 people and the seizure of 3.4 tons of cocaine in Argentina and Brazil.

Most of the drugs from Argentina seized by Spanish authorities have been camouflaged in cargo ships with myriad exports, like wind turbines and pizza ovens.

“Spain is the main entry point of South American cocaine, and we have seen increased efforts to diversify routes, often using Africa,” said Ignacio Cosidó, an expert in trans-Atlantic organized crime at the Madrid-based Strategic Studies Group.

In the most recent case, the plane bound from Buenos Aires to Barcelona stopped over in Cape Verde for refueling. Interior Minister Florencio Randazzo previously insisted that the drugs had been loaded there, not in Argentina. But Security Minister Nilda Garré acknowledged last week that airport controls “had relaxed a bit” and that she was rethinking whether the drugs could have been loaded in Argentina.

The Spanish police arrested three men, including Gustavo Julia and Gaston Miret, the pilot and co-pilots of the Challenger 604. Mr. Julia is a chief shareholder in Medical Jet and son of Brig. Gen. José Julia, who ran the Argentine Air Force from 1989 to 1993 under President Carlos Menem. Mr. Miret is a son of Brig. Gen. José Miret, who was the legal and technical secretary of the former Argentine dictator Jorge Videla. The third man arrested was Eduardo Julia, a brother of Gustavo Julia.

Santiago Giménez Olavarriaga, the lawyer for the three Argentines, said this month that his clients had no knowledge they were transporting cocaine. “They said they didn’t have anything to do with it,” Mr. Giménez said.