The warning comes just weeks before a crucial decision by the European Union on extending the GSP+ trade deal under which Sri Lankan exports have duty free access to European markets.
Sri Lanka's apparel industry, a key beneficiary of the trade deal, has said it fears losing the access because of EU concerns over alleged human rights abuses by government forces.
The EC warning came as government forces closed in on the Tigers' Kilinochchi stronghold in northern Sri Lanka after heavy fighting with aid agencies saying civilians displaced by the fighting could become victims of the violence.
"I am preoccupied by the continuing disrespect for human rights by all sides and am very concerned by reports of forced recruitment and summary executions by the LTTE," EC Commissioner for External Relations and European Neighbourhood Policy, Benita Ferrero-Waldner, said in a statement.