The European Commission has rebuffed a call from several former Soviet bloc countries for the EU to legislate against the condoning or denial of totalitarian crimes.
But the Commission, which drafts EU laws, pledged to help keep the memory of such crimes alive across Europe.
The EU is treaty-bound to combat hate crimes that target national, religious or ethnic groups.
But the Commission says crimes based on politics are a national-level matter.
Last week Lithuania's Foreign Minister Audronius Azubalis sent a letter to the Commission seeking to criminalise the approval, denial or belittling of communist crimes. He was supported by the foreign ministers of Bulgaria, the Czech Republic, Hungary, Latvia and Romania.
In a report released on Wednesday, the Commission said an independent study showed that "there is no one-size-fits-all model" in the EU for dealing with the memory of crimes committed by totalitarian regimes. The Commission-funded study was completed last year.
Many European countries, including France, Germany, Hungary and Austria, have criminalised denial of the Holocaust.
EU member states have diverse ways of dealing with past totalitarian crimes, the Commission said, so the conditions for drafting EU-wide legislation in that area "have not been met".
Article 83 of the treaty on the functioning of the EU sets out areas where Brussels can define criminal offences with a cross-border dimension, including terrorism, human trafficking and corruption. But hate crimes based on political ideology are not on the list.
It would be up to the 27 member states' governments to decide if they wanted to expand the scope of that article.
The Commission said it would, however, "within the scope of its powers... contribute to the processes engaged in the member states to face up to the legacy of totalitarian crimes".
Euro MPs' pressure
The EU Council - the grouping of member states' governments - had also asked the Commission to examine whether extra EU legislation was needed to tackle the condoning or denial of totalitarian crimes.
Pressure has come from the European Parliament too. In April 2009 MEPs adopted a resolution calling for 23 August to become a "Europe-wide Day of Remembrance for the victims of all totalitarian and authoritarian regimes".
The resolution - not legally binding - also urged the Commission and member states to boost efforts to open up secret police archives and teach European history, to make people more aware of totalitarian crimes.
The Commission noted that four EU states - the Czech Republic, Poland, Hungary and Lithuania - have explicitly criminalised the denial of crimes committed by former communist regimes, in their laws against denying totalitarian crimes.