Almost all Hungarians who voted in Sunday's referendum rejected the European Union's migrant quotas but turnout was too low to make the poll valid, frustrating Prime Minister Viktor Orban's hopes of a clear victory with which to challenge Brussels.

Hungary's maverick right-wing leader, whose hard-line policy on migration has been criticized by human rights groups but is popular at home, nevertheless said EU policymakers should heed the "outstanding" referendum outcome.

Orban said more Hungarians had rejected the migrant quotas than had voted for European Union membership in a referendum ahead of Hungary's 2004 accession to the bloc. Some 3.24 million votes were cast rejecting the quotas, compared with 2003's 3.05 million votes in favor of joining the EU.