Nearly 4,500 people have fallen sick in the south of the Democratic Republic of Congo following a toxic leak from a diamond mine in neighbouring Angola, the environment minister says.
Eve Bazaiba said 12 people had died.
She said the DR Congo would ask for reparations for the damage caused but did not specify an amount.
There has been no response so far from the mining company.
Last month’s leak from a reservoir containing heavy metal by-products caused a river to turn red, killing fish, hippos and other animals.