Gunmen burst into an unregistered drug rehabilitation centre in Mexico and opened fire Wednesday, killing 24 people and wounding seven.

Police in the north-central state of Guanajuato said the attack occurred Wednesday in the city of Irapuato. Three of the seven wounded were in serious condition.

Apparently the attackers shot everyone at the rehab center; state police said nobody was abducted.

Guanajuato is the scene of a bloody turf battle between the Jalisco cartel and a local gang, and the state has become the most violent in Mexico.

No motive was given in the attack, but Gov. Diego Sinhue said drug gangs appear to have been involved.