(ZAGREB) - A Croatian crackdown that has seen more than 100 people arrested over the sale of university diplomas is aimed at weeding out corruption, a key precondition for EU membership, analysts said.

Among those to have been detained in the widening bribes-for-grades scandal that emerged last week were 21 Zagreb university professors including the head of a parliamentary anti-corruption committee.

Prosecutors allege that professors took up to 2,000 euros (2,900 dollars) to guarantee a pass mark on a single examination, in what is shaping up to be Croatia's biggest corruption case since independence in 1991.

"This operation seems to be rather serious," said Zorislav Petrovic, head of the Croatian branch of the global anti-corruption watchdog Transparency International.

"I am very satisfied... and hope to see some concrete results," he told AFP.

"However, the most important thing is to establish a system which would prevent corruption from being repeated," he said.

Noting the "positive evolution" in the fight against corruption during the past few years, Petrovic warned that more effort was needed.

These concerns were reflected in Transparency's global corruption index, which was released on Tuesday showing Croatia still had a rating of 4.4 out of a possible 10 and ranking it 62nd out of 180 countries. Somalia was ranked in 180th position with a score of 1.0.

Croats believe the most corrupt part of their society is politics, according to the latest opinion poll conducted by local non-governmental organisation Bura.

Politicians were followed by judges, doctors and local administration employees.

Out of 1,000 people questioned, 45 percent said they had come across corruption in the medical sector, 33 percent in police and 28 percent in the judiciary.

"As far as it concerns everyday life, university circles are certainly not the priority in the fight against corruption, but any effort in that direction is very important," said political analyst Davor Gjenero.

"It is certain that the message which has been sent (by the operation), that corruption will not be tolerated any more, has chances" of succeeding to change society, Gjenero said.

Although progress had been made, "corruption remains anchored in the national conscience," he estimated.

Prime Minister Ivo Sander has said that his government is "fully supportive" of police and the state prosecutor's office.

"This operation is a part of the anti-corruption campaign that we have been leading for several years," said Sanader.

Since the operation began, more than 200 raids have been carried out, notably on apartments, offices and vehicles, and more than 120 student report cards and 81,000 euros in cash seized.

The professors, all from the economics and transport faculties, are suspected of taking bribes in return for passing students or admitting them to courses after having been monitored by police for a year.

Among those arrested was Desa Mlikotin-Tomic, a professor at the economics faculty and head of the parliamentary committee for prevention of conflicts of interests.

Twenty-nine people remained in detention, said USKOK, the national bureau for the fight against corruption and organised crime.

The amount to pass an exam ranged from 400 to 2,000 euros (575 to 2,850 dollars) while university admission cost as much as 9,000 euros (13,000 dollars).

In a report published at the end of last year, the European Union's executive commission on enlargement, said corruption was "wide-spread and deeply entrenched in society" in Balkan countries seeking EU membership.

Croatia, which opened membership negotiations in 2005, hopes to join the EU sometime around 2010.

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