PRAGUE, March 12 (Xinhua) -- The Presidents of Visegrad Group, namely, the Czech Republic, Poland, Hungary and Slovakia, met here Tuesday to celebrate their countries' accession to the North Atlantic Treaty Organization (NATO).

The Czech Republic, Poland and Hungary joined NATO on March 12, 1999, while Slovakia joined the organization five years later.

At the ceremony, Czech President Milos Zeman warned against continuing terrorism. In a interview with the Czech News Agency Monday, Zeman said terrorism is the biggest risk NATO will face in the future.

Polish President Andrzej Duda said at the ceremony that Poland takes its commitments in NATO seriously, adding that presence of Allied troops in Poland is important and necessary for the Poles to trust NATO, as they have bad historical experience.

Hungarian President Janos Ader said that the Hungarians understood the vote on NATO membership was a crucial opportunity and that missing it would be an enormous mistake.

Slovak President Andrej Kiska said present life in peace and prosperity is a result of the decision to join NATO. The Central European countries must prove that they are useful for NATO, he said, adding that they must be ready to meet its commitments and defend its allies.

The presidents confirmed the pledge of their countries to spend 2 percent of the gross domestic product on defense. Poland has already met its pledge. Zeman, Kiska and Ader said they expect their countries to spend at least 2 percent of GDP on defense by 2024.

The Visegrad Group, or V4, is a cultural and political alliance of the four Central European states that are members of the European Union and NATO for the purposes of advancing military, cultural, economic and energy cooperation with one another.