BRUSSELS (Reuters) - Hungarian Prime Minister Viktor Orban dismissed criticism on Thursday that changes his government has made to the constitution are anti-democratic, saying there was no evidence of any contravention of European Union rules.

The EU, the United States and human rights organizations have criticized the constitutional amendments and say they could limit the power of Hungary's top court and undermine democracy in the former Soviet satellite.

"Who is able to present even one single point of evidence -facts, may I say - which could be the basis for any argument that what we are doing is against democracy?" the conservative Orban told reporters ahead of an EU summit in Brussels.

"Without facts there is no sense of any general political discussion," he said.

Orban is likely to face more disapproval at the two-day summit. Many of his peers see the changes as the latest effort by the prime minister to assert power over other branches of the state.

Since returning to office in 2010, Orban has defied the EU on principles such as media freedom and central bank independence, resisted pressure from the International Monetary Fund to change economic policies, and angered foreign investors.

The latest changes restrict the constitutional court to challenging laws only on procedural grounds, not on their substance, and scrap all decisions made by the court before 2012, discarding a body of case law often used as reference.

Hungary's forint currency fell on foreign exchange markets on Thursday due to growing concerns about the constitutional amendments and an aggressive shake-up by the new governor of the central bank, a close Orban associate.

(Reporting by Luke Baker and Justyna Pawlak; Editing by Paul Taylor)