Ministers should also provide full details of what British arms were used by Sri Lankan forces during the conflict, the Committees on Arms Export Controls said in its annual report.
"We recommend that the government should review all existing licences to Sri Lanka," the report said.
It also called on ministers to provide "an assessment of what UK-supplied weapons, ammunition, parts and components were used by the Sri Lankan armed forces in the recent military actions against the Tamil Tigers."
But the lawmakers said it was "impossible" to be sure how many such weapons had been used against civilians since hostilities flared up again in 2006.
Sri Lankan security forces ended the LTTE's bloody, four-decade struggle for an independent Tamil homeland in May, as long-time Tiger chief Velupillai Prabhakaran was killed.
"Sri Lanka highlights the need for the UK government to monitor closely the situation in countries recently engaged in armed conflict," the committees' chairman, lawmake