ZAGREBb (AFP) -- Ethnic Serbs living in Croatia are worried about a growing number of attacks against members of their community that could slow the return of Serb war refugees and in turn harm the country's EU entry bid.

"Last year we saw some forms of violence -- a murder, fatal blasts or attacks on Orthodox churches -- the likes of which hadn't occurred since the 1990s" marked by the Serbo-Croatian war, said local Serb MP Milorad Pupovac.

The head of the Organization for Security and Cooperation in Europe mission here recently voiced concerns about the increasing number of such incidents in the former Yugoslav republic.

"Every three days there is one attack against members of ethnic minorities," Jose Fuentes said, stressing such incidents slowed down the return of Serb refugees that fled Croatia during and after its 1991-1995 war.

Croatia's four-year war against Belgrade-backed Serb rebels was sparked by its proclamation of independence from the former Yugoslavia in 1991.

The conflict claimed about 20,000 lives while the rebels occupied a third of Croatia and expelled almost all non-Serbs. The war ended when the rebel uprising was crushed and about 280,000 ethnic Serbs fled Croatia.

So far about 40 percent of them have returned, according to the United Nations refugee agency UNHCR.

Despite improving ties between Belgrade and Zagreb, inter-ethnic relations remain tense between their people.

Two Croatian diplomats from the country's Belgrade embassy were recently attacked in the Serbian capital, while according to Zagreb there were 65 attacks in 2005 against ethnic Serbs, with culprits found in 26 of the cases.

However the offenders in some of the most serious attacks still remain at large, including a murder of an elderly man and the "suspicious" deaths of two Serb refugees killed by explosive devices.

Serb politician Pupovac labeled as "alarming" the increase in the number of incidents that also include assaults, threats, offensive graffiti and arson attacks.

A Croatian human rights group shares Serbs' worries, warning that authorities should act more firmly.

"In a series of incidents police acted rather slowly and inefficiently thus indicating that some things could be done without any consequences," the head of the Croatian branch of the Helsinki Committee for Human rights, Zarko Puhovski, told AFP.

Puhovski agrees with the Serb leaders that a number of attacks were partly due to dissatisfaction of some people with good results of Serb parties in May 2005 local elections, notably in war-affected areas.

Also the country's two biggest rightist parties -- the ruling HDZ and the Croatian Party of Rights -- have been adopting a moderate agenda leaving part of their voters feeling betrayed and thus turning toward violence, Puhovski said.

A parliamentary committee for human rights recently condemned the "ethnically motivated incidents" and urged the government to prevent them from happening.

The ruling Croatian Democratic Union (HDZ) upon its return to power in 2003 put forward a pro-European agenda in a bid to prove it had shaken off its hardline and anti-Serb legacy.

Prime Minister Ivo Sander immediately called on all ethnic Serbs who fled the country to return and urged tolerance.

"Such statements were credible at the time but not today," Pupovac warned. The integration and return of Serbs is one of the key issues for Croatia's bid to join the European Union by 2009.

"In Brussels and Zagreb everyone has European manners but as soon as we move further away things look rather different," Puhovski said.

The Serbs are Croatia's largest minority accounting for 4.5 percent of a population of 4.4 million. Before the war they made up about 12 percent.