BUDAPEST (Reuter) - Hungary's Prime Minister Gyula Horn criticised Slovakia on Monday, saying its northern neighbour's ethnic Hungarian minority were finding it harder to exercise their rights. But he said he still hoped for better relations, telling parliament it was in Hungary's interest to improve Budapest's relationship with its neighbour. Some 500,000 ethnic Hungarians live in Slovakia and about 100,000 Slovaks in Hungary. "Slovakia's ethnic Hungarian minority has over the past few years found it increasingly difficult to enforce its rights," the Hungarian MTI news agency quoted Horn as saying. "There are plenty of sources of tension between the two countries." Tension has mounted since earlier in September when Slovak Prime Minister Vladimír Mečiar said at a mass rally in Bratislava that he had proposed the exchange of ethnic Hungarians in Slovakia and ethnic Slovaks in Hungary to Horn at an August meeting in Gyor, Hungary. Opposition parties criticised Horn for not revealing Mečiar's proposal, which they said recalled the post-World War Two years when hundreds of thousands of Germans and Hungarians were expelled from Slovakia. The tension led to the cancellation of a meeting of Slovak Foreign Minister Zdenka Kramplová and her Hungarian counterpart Laszlo Kovacs that had been planned for September 20. Horn told Parliament the government was determined to protect the rights of ethnic Hungarians beyond the border. However, he added that Hungary's interest was to improve relations. "Hungary is ready to carry on negotiations with its northern neighbour because it is not in our interest to search for an enemy or to isolate Slovakia from the process of Euro-Atlantic unification," Horn said. Hungary is among the central European countries with which both NATO and the European Union have invited for membership talks. Slovakia, once a top candidate, is not seen joining the organisations in the first stage of their enlargement.