Joaquin “El Chapo” Guzman’s sons are suspected of launching an ambush on a military convoy in Mexico that left five soldiers dead, Mexican officials say.
The assault in the northern state of Sinaloa involved grenades and assault rifles.
According to officials, the attackers succeeded in freeing a wounded drugs suspect who had been captured earlier and was being taken to hospital.
At least ten people were injured.
Sinaloa is the stronghold of the drugs gang formerly headed by Joaquin Guzman.
Officials believe the ambush may have been organized by his sons, who are believed to have taken over the running of the cartel.
“Up this point we are not certain about this group, but it is very probable that it was the sons of Chapo,” said local military commander Gen. Alfonso Duarte.
Up to 60 gunmen set upon the vehicles, beating the soldiers and freeing a drugs suspect who was being taken to hospital.
According to officials, the suspect freed by the gunman has been identified as Julio Oscar Ortiz Vega, also known as “El Kevin”.
The gunmen stole the ambulance and a military truck burst into flames during the assault.
Mexican authorities believe the sons of Guzman have been involved in other violent episodes in recent weeks.
In August, one of them was kidnapped by a rival group. Another son, Ivan, is also said to be involved in cartel activities.
El Chapo Guzman’s brother, Aureliano Guzman Loera, also known as “El Guano”, is struggling for control of drug production against the Beltran Leyva drug cartel in the remote area, officials say.
Joaquin El Chapo Guzman was arrested in January after six months on the run following his escape through a tunnel in his jail cell.
He had already escaped a maximum security facility once before, spending 13 years at large.
A Mexican judge is considering the case to have El Chapo Guzman extradited to the US.
El Chapo Guzman is expected to appeal against any decision to extradite him and his lawyers say the process could take years to come to a conclusion.