* Romania says some Hungarians running 'extremist actions'
* Government imposes entry bars before Hungarian holiday
* Tension over territorial claims to parts of Romania
By Radu Marinas
BUCHAREST, March 14 (Reuters) - Romania has barred what it says are Hungarian extremists from four different organisations from entering the country, moving to prevent possible clashes when ethnic Hungarians celebrate their national day in Romania on Saturday.
Those barred include supporters of Jobbik, a far-right Hungarian party whose popularity has surged in the run-up to a parliamentary election due to take place in Hungary on April 6, according to a recent poll.
Conflicting territorial claims over parts of Romania have sparked tensions and violence between ethnic Hungarians and Romanians in the past, and earlier this week clashes between Hungarians and police broke out in northeast Romania.
Hungary's Prime Minister Viktor Orban has courted the support of ethnic Hungarians across the border, including by giving them dual citizenship and the right to vote in Hungarian elections. That has given him a growing power base of voters.
In turn, Romania's Prime Minister Victor Ponta rebuilt his coalition and won a confidence vote with new allies from the country's main ethnic Hungarian party, after his government splintered amid a series of rows in February.
Thousands of Hungarians are expected to celebrate Hungary's National Day on March 15 in several towns across Romania, which has 1.3 million ethnic Hungarians in a population of 20 million. In a possible sign of trouble, a far-right Romanian group said earlier this week it would stage a rival rally in protest against Hungarian demands for greater autonomy.
"Romanian authorities took precautionary measures to avoid events of a kind that affect public order and national security," Monica Dajbog, a spokeswoman for the interior ministry, said on Friday, explaining the entry restrictions.
"We adopted measures to block access to Romania and asked the court to declare as persona non grata a number of Hungarian citizens who are running extremist actions in our country."
Dajbog did not specify the exact number of Hungarians that have been blocked from entering, nor the nature of their "extremist actions" on Romanian soil.
Romania will deploy about 1,000 policemen across the country to oversee the celebrations, which mark the 166th anniversary of Hungary's 1848 revolution against the Austrian Habsburgs.
Ethnic Hungarians in Romania live mostly in three counties in central Transylvania, a territory at the foot of the Carpathian mountains that was run by Budapest until 1918 but is now far from the Hungarian border.
The community in Transylvania has been a frequent bone of contention between the countries. Tensions rose last year in a dispute over the use of ethnic minority flags.
Many ethnic Hungarians would like Romania to grant them their own specific region, where they would have a greater say over local administration and education. (Editing by Matthias Williams and Mark Trevelyan)