* EU raised concern over appointment
* Bulgaria trying to show it is tackling graft
* Judge denies any wrongdoing
By Tsvetelia Tsolova
SOFIA, Nov 15 (Reuters) - Bulgaria's president blocked a judge suspected of corruption from taking a position at the country's highest court on Thursday, after EU officials raised concerns about her appointment.
The European Union's poorest country has yet to demonstrate it can impose strict rule of law and put an end to corruption, which deters investment and keeps Bulgaria outside the bloc's Schengen zone of passport-free travel.
Veneta Markovska had been approved by parliament last month to become a judge at the Constitutional Court and was to have been sworn in on Thursday for a nine-year term. But President Rosen Plevneliev left the ceremony before she could take her oath, invalidating the process.
The president and Prime Minister Boiko Borisov had appealed several times for Markovska not to take up the position after media allegations that she used her influence to help a friend escape prosecution.
Prosecutors said on Thursday they had started an investigation after a tip-off that the friend of the judge was given "a huge number of properties" and influenced the outcome of administrative court cases between 2005 and 2010, without elaborating further.
Markovska, who resigned as a deputy head of the Supreme Administrative Court to take the Constitutional Court post, has denied any wrongdoing.
"This is one of the rare examples when the president shows his moral authority," said Rumiana Kolarova, a political analyst at Sofia University.
"It is also an attempt to clear the image of the ruling GERB party, which wants to prove to Brussels it is serious about judicial reform. But it is a reactive policy - the government's will for reforms is yet to be demonstrated."
The GERB party had voted for Markovska to take the job but later tried to distance itself after the European Commission raised concerns about her appointment.
The party won power in July 2009 on pledges to fight rampant corruption. But with less than a year to go before the next parliamentary election, no senior official has been jailed on graft charges.
The European Union keeps Bulgaria's justice system under special monitoring, which is viewed by the country as a stigma that maintains its effective status as a second-class member.
A recent study showed Bulgarians gave about 150,000 bribes to civil servants every month last year, more than in 2010. (Reporting by Tsvetelia Tsolova)