Veterans of Zimbabwe's 1970s independence war, who had previously been loyal Mugabe supporters, last week issued a statement bitterly denouncing the president, who faces growing signs of opposition.
Douglas Mahiya, spokesman for the War Veterans' Association, was arrested yesterday in Harare, according to the Zimbabwe Lawyers for Human Rights (ZLHR) group.
"Information presently at hand is that the police are charging him with subverting a constitutional government and insulting the office of the president," the lawyers said.
The association's secretary-general, Victor Matemadanda, was also taken from his rural home in Gokwe, north west Zimbabwe, after being summoned for police questioning.
"His whereabouts are currently undetermined, as are the charges or allegations against him," ZLHR said.
Recent demonstrations, the largest in many years in Zimbabwe, have been triggered by an economic crisis that has left banks short of cash and the government struggling to pay its workers.
More than 90 per cent of the population is not in formal employment after years of economic decline under Mugabe's rule.
"When we find out who the people were, the party will discipline them. The punishment will be severe," Mugabe said in a speech yesterday to supporters outside the headquarters of the ruling ZANU-PF party.
In a dramatic change of stance, the liberation war fighters last week vowed not to support Mugabe, who has been in power since 1980, if he sought re-election in 2018.
"You can't maintain a dictatorship by arresting people for speaking their mind," Rugare Gumbo, a war veteran and former senior government official, told AFP.
Starting in 2002, the veterans led the government-backed seizures of white-owned commercial farms, in what Mugabe said was a reversal of imbalances from the colonial era.