László Sólyom, the Hungarian president, described the decision as "unprecedented" and "inexcusable".
Robert Fico, the Slovak prime minister, responded that the attempted visit by Hungary's head of state was "a provocation" and "a violation of international law".
Sólyom had been due to attend the unveiling of a statue of the medieval Hungarian king, Saint Stephen, in the southern town of Komarno, on the River Danube. The visit, at the invitation of a local civil society organisation, was considered "unofficial". It was also aimed at marking 20 August, the Hungarian national day, known as St. Stephen's Day.
Slovak Foreign Minister Miroslav Lajcak said the visit was ill-intended, as it coincided with the commemoration by Slovaks of the 1968 invasion of Czechoslovakia by five armies, including Hungary's.
Returning from the bridge, which lies on Hungarian territory, Sólyom insisted that the Slovak authorities had been informed about the planned ceremony more than two months ago, and had been cooperative until the last few days.
"I hope that the hysteria, which broke out at the highest levels during the past two days, does not reflect the emotions of the Slovak side," Sólyom said. He added that his country would not leave this latest development unanswered, and that Hungarian diplomacy would make every effort to express the significance of the affair at international level.
EU asked to take a position
The European Union lacks any mechanism to prevent one of its member states from freely overstepping the legal boundaries of another, and the European Parliament should take up the issue to ensure that this does not happen in future, Hungary's Foreign Minister Péter Balázs said today.
Balázs added that it would be inconceivable for, say, the German head of state to be denied entry into France, the Hungarian press reported.
However, Peter Weiss, Slovakia's ambassador to Budapest, told the commercial station TV2 on Sunday evening that Hungary should not attempt to ask for EU help. The issue should be resolved bilaterally, he said.