The unidentified foreigners were "held for questioning by the security brigade... For an hour and a half and roughed up" yesterday night, Tarek Mitri told a press conference in the capital.
Mitri denounced the "unacceptable" treatment of the men, who he said have diplomatic immunity.
The men were carrying arms licensed by the interior ministry and were returning from the eastern town of Al-Baida, where they had travelled to prepare a visit by Mitri.
He said the incident occurred at Tripoli's Al-Hadhba complex, where officials from the regime of slain dictator Moamer Kadhafi are being held and tried.
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Yesterday night's incident came hours after a senior Swiss staffer of the Red Cross was gunned down in the city of Sirte, Kadhafi's hometown on the central coast.
Libya has descended into almost total lawlessness since the 2011 uprising that ousted Kadhafi. The government has almost no power over the many armed brigades that fought to overthrow the dictator and have since carved out their own spheres of influence.