HARARE, Zimbabwe — Zimbabwe police charged a United States citizen with subversion for allegedly insulting President Robert Mugabe on Twitter as a ‘‘sick man,’’ lawyers said Friday. The offense carries up to 20 years in prison.

This is the first arrest made since Mugabe last month appointed a minister for cybersecurity, the Zimbabwe Lawyers for Human Rights said, in a move criticized by activists as aimed at clamping down on social media users. Zimbabwe last year saw its biggest antigovernment protests in a decade.

Police picked up 25-year-old Martha O’Donovan on Friday in the capital, Harare, the US Embassy said.

Police accuse O’Donovan of tweeting ‘‘We are being led by a selfish and sick man,’’ said her lawyer, Obey Shava, of Zimbabwe Lawyers for Human Rights. O’Donovan, formerly of Nw York, has been charged with undermining the authority of or insulting the president, and subverting a constitutionally elected government. She has denied the allegations.

ASSOCIATED PRESS