TORONTO -- An elderly man has launched yet another challenge to his loss of citizenship and potential deportation for lying to Canadian authorities about his membership in a Second World War Nazi death squad.

The notice of appeal from Helmut Oberlander comes even though a Federal Court judge recently ruled that Ottawa had acted reasonably in the case and limited his ability to appeal.

Lawyers for Oberlander, 94, of Waterloo, Ont., refused on Friday to discuss the appeal notice filed this week, so the legal underpinnings of their action were not immediately evident.

However, in a letter sent to the court, the federal government made it clear that it objects to the filing. The letter further asks that the Federal Court of Appeal registry forward the appeal notice to the court for review.

The Ukraine-born Oberlander, who came to Canada in 1954 and became a citizen six years later, has steadfastly maintained he was just 17 when he was forced on pain of execution to join the Nazi death squad Einsatzkommando 10a, known as Ek 10a. The squad was responsible for killing close to 100,000 people, mostly Jewish.

In June 2017, the government revoked the retired businessman's citizenship for the fourth time since the mid-1990s, prompting his current effort to stave off deportation.

Earlier this month, Federal Court Judge Michael Phelan lifted a stay on his earlier decision that the government had been reasonable in stripping citizenship from Oberlander.  Phelan found that Oberlander had misrepresented his war-time activities even though no evidence existed that he took part in any atrocities.

"It is uncontested that Oberlander obtained his Canadian citizenship by false representation or by knowingly concealing material circumstances by failing to disclose involvement in the SS at the time of his immigration screening," Phelan wrote. "There is no doubt that to have done so would have resulted in the rejection of his citizenship application."

Phelan also refused to "certify a serious question of general importance" that would have allowed Oberlander to appeal the merits of the decision itself under immigration law.

Oberlander may yet be able to persuade the Federal Court of Appeal to hear the case on grounds outside of the Immigration Act but the higher court generally hears only a fraction of cases decided by Federal Court.

In September, Immigration Minister Ahmed Hussen said Canada should never be a "safe haven for war criminals and people who've been accused of crimes, who've committed crimes against humanity."