Blogger Caruana Galizia, who was 53 when she was killed in a car bomb attack on October 16, had made repeated and detailed corruption allegations against both Muscat's inner circle and the opposition.
Muscat said police and the military were involved in an operation following a weeks-long investigation into the high- profile murder.
"During this operation, 8 persons were arrested" the statement said, adding that they faced "reasonable suspicion in connection with involvement in the murder" of Caruana Galizia.