The initiative was organised by the Direito a Morrer com Dignidade (Right to Die with Dignity) movement.

The Left Bloc, the third largest party in parliament and one of the groups whose support enables the survival of Portugal's minority Socialist government, has promised to table a bill on the subject soon after the debate on the petition.

Public discussion of the issue was triggered last year when the head of Portugal's national nurses' association claimed that some doctors in the national health service had connived in assisted suicides for terminally ill patients at public hospitals, despite the fact that euthanasia is not legal in the country.

The Health Ministry on Monday ordered an urgent inquiry into the allegations.

At present, helping a patient to die is considered homicide and can carry a penalty of up to three years in prison.