US Principal Deputy Assistant Secretary for South and Central Asian Affairs Donald Camp ended a visit to Sri Lanka on Tuesday by saying Washington had "encouraged the EU to list the LTTE" as a terrorist group.
"We think the LTTE is very deserving of that label.
We think it will help cut off financial supplies and weapons procurement and the like," he said.
The US banned the LTTE in 1997, five years after India outlawed the group, holding it responsible for the assassination of former Indian prime minister Rajiv Gandhi.
Canada labelled the Tigers a "terrorist" group last month.
The EU freezes the assets of groups on its terrorist list.
The designation also allows for special cooperation measures to combat them.
Sri Lankan Foreign Minister Mangala Samaraweera said in Tokyo on Thursday that he hoped Sri Lanka's donors would use their influence on the Tigers to stop their attacks and resume talks.
He was to hold talks with his Japanese counterpart Taro Aso in Tokyo o