Tension has increased between Slovakia and Hungary, following recent attacks on members of Slovakia's sizeable Hungarian minority.
Hungarian Prime Minister Ferenc Gyurcsany condemned what he described as "atrocities" and rising xenophobia in Slovakia. Both are EU member states.
Hungary's foreign ministry summoned the Slovak ambassador on Monday to protest against the attacks.
Slovakia has promised to take action, but says Hungary is overreacting.
Nearly 600,000 ethnic Hungarians live in neighbouring Slovakia, making up about 10% of the country's population.
The row erupted after a young ethnic Hungarian woman was beaten up in the Slovak town of Nitra last Friday, apparently after being heard speaking Hungarian on her mobile phone.
A day later, an ethnic Hungarian teenager was attacked in the town of Sladkovicovo, allegedly for speaking Hungarian.
The party representing Slovakia's Hungarians, the SMK, said that in recent weeks gangs of young Slovaks had been entering bars and intimidating Hungarian speakers.
In Hungary, the Slovak embassy has been daubed with graffiti, and anti-Slovak banners have been unfurled at football matches.
Mr Gyurcsany described the attacks as "atrocities" during a televised debate with Slovak Prime Minister Robert Fico on Tuesday.
Mr Fico promised to take action, but has so far failed to condemn the attacks.
Slovakia accused Hungary of an overreaction to the incidents, which was creating an "atmosphere of tension" between the two countries.
Tensions have been rising since the vehemently anti-Hungarian Slovak National Party (SNS) joined the government in Bratislava in June, the BBC's European affairs analyst Jan Repa says.
The SNS leader, Jan Slota, has referred to Hungarians as a "cancer" and expressed regret that they had not been expelled after World War II.
The Hungarian-Slovak relationship is full of psychological tension and ambiguity, our analyst says.
For the best part of 1,000 years, Slovakia was the northern, mainly Slav-speaking, part of the kingdom of Hungary.
When a Slovak national movement finally got under way in the 19th Century, it was vigorously suppressed by the Hungarian authorities.
When the Austro-Hungarian Empire collapsed in 1918, the Czech army carved out an area of northern Hungary - including a belt of Hungarian-speaking territory - and incorporated it into the new state of Czechoslovakia.
Hungary re-annexed the mainly Hungarian-speaking districts during World War II, which then reverted to Czechoslovakia at the end of the war.
In 1993, Czechoslovakia broke up into separate Czech and Slovak states.
Slovakia proclaimed itself "the state of the Slovak nation", which some Slovak Hungarians took to imply that they were second-class citizens, Jan Repa reports.