Rakapaksa’s second son, Yoshitha, a 27-year-old naval officer, was arrested with four others, including Rakapaksa’s spokesman and a brother of Ports and Shipping Minister Arjuna Ranatunga.
A local court ordered those detained to stay in custody until February 11, police spokesman Ruwan Gunasekera said.
President Maithripala Sirisena is under pressure to act on allegations of corruption against Rajapaksa and those who served his administration, especially from civil society organisations which backed Sirisena against Rajapaksa in last year’s election.
Rajapaksa is still popular among many ethnic majority Sinhala Buddhists who credit him with ending a 26-year-war against Tamil Tiger rebels in 2009.
Yoshitha, who was Sri Lanka’s national rugby team captain when his father was the president, was arrested after more than six hours of questioning by police, two officials told Reuters.
Rajapaksa, who went to the local court to hear the order against his son, angrily condemned the police’s use of the money laundering act to arrest his son.
“Today they (the government) have used that act which we brought to deal with terrorists to put the son of the person who eradicated terrorism behind bars,” Rajapaksa told reporters.
“We have trust in the judiciary system and expect the justice will prevail. All these (actions) are to take revenge of me.”
Rajapaksa, now an opposition legislator, is being investigated for misappropriation of money in a state-run television channel during the 2015 presidential polls.
Many Rajapaksa sympathisers believe these allegations were brought to tarnish his name and influence voters against him.