He revealed suspects of murders and war crimes that were sheltered in embassies by the former government.
Mangala Samaraweera told parliament a deputy ambassador posted to Brazil and two staffers sent to Germany were among those suspected of murders and war crimes that were sheltered in embassies by the former government.
"Many of our embassies had become safe houses for criminals involved in killings as well as grave human rights violations at home," Samaraweera told parliament.
"They were rewarded by giving places in our embassies abroad."
The minister said the envoy sent to Brazil by the Mahinda Rajapakse government was accused of murdering another embassy employee and committing human rights abuses in the dying days of the decades-long conflict, which ended in 2009.
Meanwhile the two given postings in Berlin were key suspects in the 2009 high-profile assassination of newspaper editor Lasantha Wickrematunga, a Rajapakse critic, he added.
Both have since been remanded in custody over the murder, which triggered international outrage.
Local media have reported that another suspected criminal was nominated for a diplomatic posting in Thailand shortly before Rajapakse's re-election in 2010.
The former president and several members of his family are under investigation for large-scale fraud and murder during his presidency, which ended in 2015.
Sri Lankan criminal investigators have told an ongoing court hearing that a death squad overseen by Rajapakse's brother was responsible for targeting the president's political opponents and critics, including Wickrematunga.
The Rajapakse family have denied any wrongdoing and have accused the new government of a political vendetta.
Rajapakse's regime faced international censure after it was caught smuggling into Britain a pro-Colombo Tamil warlord, Vinayagmoorthy Muralitharan, in September 2007 using a Sri Lankan official passport.
Muralitharan who is also known as colonel Karuna was sentenced for nine months imprisonment and the incident soured relations between the two countries and led to Sri Lanka's isolation by Western nations over its rights record.