Sirisena has insisted that as minister of defence and law and order he was unaware of precise intelligence warnings from India about the attack on April 21.
President Sirisena appointed the committee on April 22 to probe into the Easter bombings and identify its root causes along with other related matters.
The cabinet of ministers approved a proposal by the acting justice minister, which will also see offenders fined one million rupees (USD 5,715), the government said in a statement.
Official sources said Hashim came to the attention of the authorities following a violent clash with a moderate Muslim group in his village in eastern Sri Lanka two years ago.
The two-member team is in the Sri-Lankan capital to find out any possible links between the terrorist modules and the terrorists involved in the deadly Easter Sunday bombings in Sri-Lanka.
The government imposed a nationwide curfew Monday and temporarily blocked social media and messaging apps.
Sri Lankan radicals who had pledged allegiance to the Islamic State group have been blamed for the April 21 bombings against three Christian churches and three luxury hotels.