The European Union has banned Sri Lanka's Tamil Tiger rebels from visiting member states.
Mr Kadirgamar's murder was shocking, the EU said.
A strongly-worded statement condemned the killing of Foreign Minister Lakshman Kadirgamar in August. The rebels denied involvement in the death.
The EU also said it was considering listing the Tigers as terrorists. They are already listed as such in several countries, including the UK and US.
The August killing was a major setback to peace moves which stalled in 2003.
The EU condemned what it called "the continuing use of violence and terrorism" by the rebel organisation, in particular the "shocking" assassination of the foreign minister.
The statement said the Liberation Tigers of Tamil Eelam (LTTE) were endangering the peace process, as well as damaging their own credibility and standing.
"The European Union has also agreed that each member state will, where necessary, take additional national measures to check and curb illegal or undesirable activities (including issues of funding and propaganda) of the LTTE, its related organisations and known individual supporters," the statement added.
A spokesman for the rebels, Daya Master, told the Associated Press: "We are not a terrorist organisation."
Both the government and Tigers had agreed to talks following the foreign minister's murder.
But with disagreement over the venue and presidential elections drawing closer, the BBC's Dumeetha Luthra in Colombo says a meeting now looks increasingly unlikely.