BUCHAREST, May 31 (Reuters) - Romania is dragging its feet in investigating four suspected Romanian Nazi war criminals discovered by the Simon Wiesenthal Center more than a year ago, the prominent Jewish group said on Wednesday.

The four are among 18 Romanians who were the subject of research by the Nazi-hunting group as part of its "Operation: Last Chance", which offers financial rewards in an effort to catch the few perpetrators of the Holocaust still alive.

"It would be a mockery of the memory of the victims of the Holocaust in Romania if those responsible for their deaths were not held accountable due to the failure of the Romanian judicial system to bring them to trial," the group's chief Nazi hunter Efraim Zuroff said in a letter to Romanian prosecutors.

"The fact that the investigation of these cases still has not been completed ... is a cause for grave concern," he said.

Romanian prosecutors were not immediately available to comment.

Romania, which shed communism in 1989, has only just started coming to terms with its role in World War Two, admitting for the first time in 2003 that it played a role in the Nazi Holocaust.

Under pro-Nazi Marshal Ion Antonescu, Romania became a German ally in 1940 but switched sides shortly before the end of the war.

Schoolchildren were not taught about the Holocaust during the communist era, and the subject was introduced only in 2004 after a row with Israel.

Between 280,000 and 380,000 Romanian and Ukrainian Jews were killed by Romanian civilian and military authorities in Romania and territories it controlled during World War Two, many of them slaughtered in pogroms or murdered in labour camps or death trains.

A further 135,000 Romanian Jews living in Transylvania, then part of Hungary, and 5,000 Romanian Jews living outside Romania were also killed. Over 25,000 Romanian Roma were deported, of whom 11,000 died.

Romania is near the bottom of a list the Wiesenthal Center has drawn up ranking countries' prosecution of war criminals by effort and results.

Romania, a poor Balkan state, is struggling to reform its judicial system as part of its drive to join the European Union next year, but its efforts are marred by crumbling infrastructure, poor training and endemic corruption.

Recent reforms carried out by the centrist government have improved the judiciary and won praise from Brussels, but many observers say the real impact has yet to be seen.

Only 13,000 Jews now live in Romania, which was home to 750,000 before the war.

Reuters, 31.05.2006