Hungary's president was banned from visiting a part of Slovakia with a large ethnic Hungarian population Friday, officials said.
Slovak Prime Minister Robert Fico said the Hungarian Embassy had been informed that the country's president, Laszlo Solyom, would not be allowed to visit the border town of Komarno to unveil a statue of St. Stephen, Hungary's first king.
Slovak leaders have called the trip "a provocation" because Friday was the 41st anniversary of the 1968 Soviet-led invasion of what was then Czechoslovakia. This involved armies from five Warsaw Pact countries including Hungary.
Solyom called Friday's move "an unprecedented step between allies, which can't be explained." Solyom spokesman Ferenc Kumin said the president decided not to cross the border because Slovakia said he would be breaking the law if he went ahead with the visit.
Solyom said he sent a letter Friday to Slovak counterpart Ivan Gasparovic reminding him that Hungary had already apologized for its involvement in the invasion and claimed that Slovak diplomats earlier had not objected to the Komarno visit.
Gasparovic had made a last-minute appeal asking Solyom to cancel the trip.
Relations between the countries have been strained mainly by differences over the rights of about 520,000 ethnic Hungarians in Slovakia. They have worsened especially since 2006 when Jan Slota's ultra-nationalist Slovak National Party became part of Slovakia's government coalition.
Fico accused Hungary of staging "an unprecedented campaign" against the country's new language law, which Hungary says limits minorities' rights.
The new law takes effect Sept. 1 and calls for fines of up to euro5,000 (about $7,000) for anyone misusing the Slovak language and limits the use of Hungarian in public. Hospital employees, for example, would only be able to speak to patients in Hungarian if at least 20 percent of the locality's population is ethnically Hungarian.
Ethnic Hungarians in Slovakia live mostly on territories Hungary lost in post-World War I peace treaties.
Associated Press writer Pablo Gorondi in Budapest, Hungary, contributed to this report.