Sri Lanka's defence secretary, Karunasena Hettiarachchi said the TID's arrest of former LTTE commanders is in relation to the reported finding of a suicide vest and unexploded explosives in Jaffna.
In an interview with the BBC, Mr Hettiarachchi said he could not make any comment until the investigation was over.
"After the investigations over and a reports are submitted only we can make a statement," he was quoted by Colombo Page as saying.
Denying there was any threat to national security, he added, "we currently do not have such a threat but if there is such a situation we will be vigilant."
The former head of the LTTE's Trincomalee intelligence wing Thalaiarasan was taken into custody on Monday, whilst the former LTTE commander, Kanathippillai Sivamoorthy, known as Nagulan, was abducted in Jaffna on Tuesday and was found later in custody. His detention came shortly after the arrest of the LTTE cadre Damotharan Jayakanth by Sri Lanka’s Terrorist Investigation Department (TID) as well as the former LTTE commander, Ram, who was earlier reported as abducted in the Eastern province but found to have been detained by Sri Lanka's Terrorism Investigation Division (TID).