(CNN) -- An elderly man suspected of Nazi war crimes has been arrested in Hungary, prosecutors said Wednesday, after a worldwide Jewish rights organization discovered him living in Budapest.

Laszlo Csizsik-Csatary is accused of sending more than 15,000 Jews to the Auschwitz concentration camp in the spring of 1944, the Simon Wiesenthal Center said.

The center considers him its most-wanted Nazi war criminal.

The Simon Wiesenthal Center found Csizsik-Csatary as part of its Last Chance project, said Efraim Zuroff, director of the center's Israel office.

Csizsik-Csatary served as a senior Hungarian police officer in the city of Kosice, which is now in Slovakia but was under Hungarian rule in the 1940s, the center said.

"He was a commander of a ghetto," Zuroff said.

Csizsik-Csatary participated in the deportation of 15,700 Jews to the Auschwitz concentration camp in 1944, witnesses have told the center. He also played a role in "deportations to the Ukraine to be killed: 300 Jews," Zuroff said.

"We found eyewitnesses on three different continents," Zuroff said. Those witnesses told the center about Csizsik-Csatary's cruelty to Jewish detainees and his role in the deportations to Auschwitz and Ukraine.

Csizsik-Csatary denied the allegations to a reporter from the British tabloid The Sun.

A witness to the August 1941 Ukraine deportations had nine family members who were deported, Zuroff said. Csizsik-Csatary made sure four of them were brought back from forced labor with the Hungarian army so they would be deported and killed, according to Zuroff.

During the Auschwitz deportations, Csizsik-Csatary "forced these girls to dig a ditch with their hands -- young Jewish girls." Two of the center's witnesses were survivors of that deportation, he said.

Using the last name Csizsik, Csizsik-Csatary arrived in Canada in 1949, telling immigration officials he was Yugoslavian, according to The Toronto Star newspaper.

Canadian authorities later investigated allegations that he had lied to immigration authorities about his past when he arrived there. Canada revoked his citizenship in 1997 and initiated an investigation.

As deportation proceedings were under way, Csizsik-Csatary voluntarily left the country.

Csizsik-Csatary returned to Hungary upon leaving Canada, Zuroff said.

"Hungarian authorities knew that he was back," he said.

Authorities in Hungary launched an investigation in September 2011 after receiving information from Zuroff regarding Csizsik-Csatary's residence in Budapest and his role in the Auschwitz deportations, the center said.

CNN's Jo Shelley and journalist Flora Hevesi contributed to this report.