Five musicians who disappeared in the Mexican city of Reynosa, near the US border, were murdered by suspected drug cartel members, Mexican authorities have said.

Nine alleged members of the notorious Gulf Cartel have been arrested on suspicion of murder, according to Irving Barrios Mojica, attorney general for the Mexican state of Tamaulipas.

The musicians – known as Grupo Fugitivo – were kidnapped while travelling to a private event on 25 May, Barrios Mojica said. Soon after, their relatives reported receiving ransom demands.

Investigators are working to establish a motive for the killings.

The musicians were aged between 20 and 40, and often played at local parties and dances.

Nine firearms and two vehicles were also seized during the arrests.

Grupo Fugitivo performed a range of regional Mexican music, a genre which includes corridos – songs that have historically been used to pay homage to drug cartels and their leaders.

It is not immediately clear if the group was targeted because of their music, or were caught up in the violence that has long beset Tamaulipas, where the Gulf Cartel has a strong presence.

The Trump administration has designated the Gulf Cartel, alongside several other criminal groups, a “global terrorist organisation”.

In January, the US embassy in Mexico issued a level 4 travel advisory, the highest level, warning its citizens not to travel to several Mexican cities, including Reynosa.

It cited the risk of “crime and kidnapping” and “increasingly frequent gun battles occurring in and around” the city.

“Heavily armed members of criminal groups often patrol areas of the state and operate with impunity particularly along the border region from Reynosa to Nuevo Laredo,” the US state department said.

“In these areas, local law enforcement has limited capacity to respond to incidents of crime.”