A top court of the European Union has annulled the bloc's decision to keep the Palestinian Islamist movement Hamas on a list of terrorist groups.
The decision had been based not on an examination of Hamas' actions, but on "factual imputations derived from the press and the internet", judges found.
The court said the move was technical and was not a reassessment of Hamas' classification as a terrorist group.
It said a funding freeze on the group would continue for the time being.
Hamas dominates Gaza and fought a 50-day war with Israel in the summer. Under its charter, the movement is committed to Israel's destruction.
Responding to the ruling Israeli Prime Minister Benjamin Netanyahu said Hamas was a "murderous terrorist" group which should be put back on the list immediately.
Israel, the United States and several other nations have designated Hamas a terrorist organisation due to its long record of attacks and its refusal to renounce violence.
Hamas, which was founded in 1987, won Palestinian parliamentary elections in 2006 and reinforced its power in Gaza the following year after ousting its Fatah rivals.
Its supporters see it as a legitimate resistance movement against Israel, with whom it has fought for years.
In December 2001, the Council of the European Union - representing the governments of member states - adopted a "common position" and a regulation to combat terrorism.
It established a list of designated entities and people whose funds would be frozen. Hamas' military wing, the Izz al-Din Qassam Brigades, was named on the initial list, and its political wing was added two years later.
Hamas contested the decision and on Wednesday the EU's General Court found it had been "based not on acts examined and confirmed in decisions of competent authorities but on factual imputations derived from the press and the internet".
The court said it was therefore annulling Hamas' designation but would temporarily keep existing measures against the group "in order to ensure the effectiveness of any possible future freezing of funds".
This would be maintained for three months, or, if an appeal is brought before the European Court of Justice, until it was closed, it added.
"The court stresses that those annulments, on fundamental procedural grounds, do not imply any substantive assessment of the question of the classification of Hamas as a terrorist group within the meaning of the common position."
Hamas' lawyer, Liliane Glock, said she was "satisfied with the decision".
"Every decision since 2001 imposing restrictive measures, including on the armed wing, have been annulled. I believe that this judgement shows the whole world that it exists and is legal," she told the AFP news agency.
The Israeli prime minister said he expected the Council of the European Union to "immediately put Hamas back on the list".
"Hamas is a murderous terrorist organisation which in its charter states its goal is to destroy Israel," he added in a statement.
The ruling comes hours before the European Parliament is expected to vote on recognition of Palestinian statehood, after the parliaments of several member states took a similar step.