Clashes in four Brazil jails kill 40

At least 40 inmates were killed in four jails in northern Brazil on Monday over an apparent gang dispute, authorities said, in the latest wave of violence to rock the country's severely overpopulated and deadly prison system.

The victims appeared to have been killed by "asphyxiation," the Amazonas state government said in a statement, a day after 15 people were killed in one of the prisons.

Officials had initially put the number of dead at 42, but later revised the number to 40.

At least 25 of the victims were found in the Antonio Trindade Penal Institute near Manaus, the capital of Amazonas, where all four prisons are located.

No guns or knives were used in the killings, which prison officials said appeared to have been sparked by a "rift between prisoners who belonged to the same criminal group and were involved in drug trafficking in the state."

The federal government has dispatched reinforcements to boost security in the jails.

An investigation launched into Sunday's mass killing at the Anisio Jobim Penal Complex, in which some of the prisoners were stabbed with sharpened toothbrushes during visiting hours, has been widened to include Monday's deaths.

Four of those killed in the latest violence were found at the Anisio Jobim jail, which was also the scene of a prison rebellion that lasted almost 20 hours and left 56 people dead in January 2017.

Another five were killed at the Provisional Detention Center for Men and six died at the Puraquequara Prison Unit.

"The fact that the killings were coordinated across four separate prisons... suggests that this was a settling of scores," Robert Muggah, research director at the Igarape Institute think tank in Rio de Janeiro, told AFP.