THE HAGUE, NETHERLANDS -- A lawyer for Ratko Mladic told a UN court Tuesday that the former Bosnian Serb military chief may not be mentally fit to take part in an appeal hearing against his convictions for crimes including genocide committed throughout the 1992-95 Bosnian War and warned that pressing ahead could lead to a miscarriage of justice.

"I am unable to meaningfully gain instruction from Mr. Mladic, nor be assured that he is able to meaningfully participate and follow" the proceedings, lawyer Dragan Ivetic told the hearing that was held partially by video conference because of coronavirus measures.

He said the two-day hearing that started Tuesday shouldn't proceed without an analysis of 77-year-old Mladic's fitness to participate. At a hearing last month, Mladic's legal team warned that the former general could be suffering from early stage dementia.

"It is a denial of due process to sentence or proceed criminally against someone who is incompetent to stand trial," Ivetic said.

The hearing proceeded despite Ivetic's objections. Mladic was in court and initially wore a face mask, before pushing it below his chin and then removing it altogether.

Lawyers for Mladic have repeatedly complained about his ill health, but in a written ruling before Tuesday's hearing, judges said that the lawyers hadn't "substantiated that Mladic is unable to communicate, consult with his counsel, and/or understand the essentials of proceedings."

Mladic was convicted by a U.N. war crimes tribunal in 2017 and sentenced to life imprisonment for masterminding crimes by Bosnian Serb forces throughout the war that left 100,000 dead, an overwhelming majority of them Bosnian Muslim civilians. He is asking the U.N. appeals mechanism to overturn all his convictions and acquit him or order a retrial.

Prosecutors, meanwhile, are appealing against Mladic's acquittal on a second count of genocide related to "ethnic cleansing" campaigns to drive Muslims and Croats out of territory claimed by Serbs in Bosnia.

Mladic evaded justice for nearly 16 years after his indictment in July 1995 until he was arrested in Serbia in May 2011 and transferred to The Hague to stand trial.

His former political master, Radovan Karadzic, also was convicted of crimes including genocide for overseeing atrocities by Bosnian Serb forces during the war. His appeal was rejected almost in its entirety and judges raised his sentence from 40 years to life imprisonment.

06:01ET 25-08-20