Jerusalem - Germany has over the past year significantly improved its efforts to bring to justice the world's last living Nazi war criminals, the Simon Wiesenthal Centre said Tuesday.

But others, including Austria and several Eastern European and South American states, are still failing to do so, the organization said in its annual report evaluating countries for their efforts to track down, prosecute and try ex-Nazis residing within their borders.

Only the United States received an A, while Germany, Serbia and Spain were the only three countries to receive a B in the report.

Austria, Australia, Estonia, Hungary, Lithuania, Sweden, Syria and the Ukraine received an F because they refuse in principle to investigate and prosecute aging Nazis, whether for ideological or legal reasons such as statutes of limitations, according to the report.

The report noted the "ongoing and consistent success" of the US Justice Department's Office of Special Investigations in finding, revoking the citizenship and subsequently deporting to their countries of departure former Nazis who have settled in the US since the war.

The Wiesenthal Centre, whose goal is to hunt down former Nazis, praised Germany for the March indictment at a Munich court of Ukrainian-born Ivan Demjanjuk, dubbed "Ivan the Terrible," over the mass murder of Jews at Poland's Sobibor Nazi death camp.

The centre said it was "most disappointed by Hungary's failure hereto to bring to justice Sandor Kepiro, a Hungarian officer now in his 90s accused of carrying out the mass execution of hundreds of civilians in Novi Sad, Serbia in January 1942. He was tried and convicted but never served his punishment, although exposed by the Wiesenthal Centre as living in Budapest in the summer of 2006.

The centre also published its updated, top 10 list of most-wanted Nazi war criminals, headed by Demjanjuk and followed by Kepiro as number two.

Aribert Heim, a Nazi physician known as "Dr Death" for allegedly murdering hundreds of inmates of Mauthausen Concentration Camp by lethal injection, topped the list last year.

But Germany's ZDF television channel and the New York Times reported in February they had information he died in Cairo in 1992.

Although no longer number one, the Wiesenthal Centre placed him in a separate category at the top of the list, with Director Efraim Zuroff saying he had "serious question marks" about the reports on his death.

"For us the case isn't closed. It definitely isn't closed," Zuroff told the German Press Agency dpa from Jerusalem. "We are continuing our efforts to find him."

The Wiesenthal Centre publishes its Status Report on the Worldwide Investigation and Prosecution of Nazi War Criminals each year on the occasion of Israel's Holocaust Remembrance Day, which the country marked Tuesday to commemorate the deaths of 6 million Jews during World War II. (dpa)