Muscat provided no other concrete information about the arrests or suspects, citing concerns that anything he says could derail any prosecution.
"In October, Caruana Galizia was killed by a auto bomb so big it hurled the vehicle almost 90 yards into a field".
The head of the Parliament's delegation, socialist lawmaker Ana Gomes, said the murder "was aimed at instilling fear in everyone, especially those involved in investigating and prosecuting cases of money laundering and corruption".
The arrests came seven weeks to the day after the assassination of Daphne Caruana Galizia.
The editors of eight of the world's largest news organisations, including the BBC, called for the European Commission - the EU executive - to investigate the 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. Shortly afterward, he tweeted that two others had been arrested.
A court hearing has been scheduled for Tuesday, when the police can officially file charges and the suspects can enter a plea. The suspects then can either plead innocent or guilty.
Europol, the European Union's police agency, sent a team of organized crime experts to help Maltese police investigate the assassination, joining the Federal Bureau of Investigation and Dutch forensic experts.
The island nation has a reputation as a tax haven in the European Union and has attracted companies and money from outside Europe as well.
She was well-known in the small island country for her popular blog, Running Commentary, where she highlighted alleged high-level corruption by politicians across party lines.
Last week, a visiting delegation of European Parliament lawmakers left the island expressing concerns over the rule of law in the country and issued a warning that the "perception of impunity in Malta can not continue".
The Mediterranean country observed a national day of mourning in her honor and has offered a 1-million-euro (1.19 million USA dollar) reward for information about her murder.
Half an hour before the explosion, Caruana Galizia wrote on her blog: "There are crooks everywhere you look now". "As soon as I learned about this barbaric act, I said that we will leave no stone unturned".