Searches were carried out on more than 40 properties as part of the action, staged by the PJ police’s national anti-terrorism unit.
It targeted “problematic” neighbourhoods in Loures, Amadora and Leiria and saw a number of weapons – many bought on the black market and often used in violent crimes such as thefts and murders – being confiscated and removed from the streets.
The UNCT, which specialises in fighting violent organised crime, launched it action at around 7am on Tuesday morning.
A statement from the PJ police added that some of those who were arrested in the raids had existing criminal records.