FILE -- In this Wednesday, Nov. 1, 2017 file photo, Zimbabwean President Robert Muagbe addresses mourners at the Heroes Acre in Harare. Lawyers and a U.S. Embassy official have said Friday Nov. 3, 2017, Zimbabwe police have arrested a United States citizen, named as Martha O'Donovan, for allegedly insulting President Robert Mugabe on Twitter. (AP Photo/Tsvangirayi Mukwazhi, File)

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

It was the first arrest made since Mugabe last month appointed a minister for cybersecurity, the Zimbabwe Lawyers for Human Rights said, a move criticized by activists as aimed at clamping down on social media users. Zimbabwe was shaken last year by the biggest anti-government protests in a decade.

Police picked up 25-year-old Martha O'Donovan on Friday morning in the capital, Harare, U.S. Embassy spokesman David McGuire told The Associated Press.

Police accuse O'Donovan of tweeting "We are being led by a selfish and sick man," from the Twitter handle @matigary, said her lawyer, Obey Shava with Zimbabwe Lawyers for Human Rights. The tweet had a photo illustration of the 93-year-old Mugabe with a catheter, the charge sheet said.

O'Donovan has been charged with undermining the authority of or insulting the president, Shava said. She later said O'Donovan faced additional charges of subverting a constitutionally elected government.

"I deny the allegations levelled against me as baseless and malicious," O'Donovan said in a signed statement shown to the AP.

O'Donovan had been working with local social media outlet Magamba TV, whose target audience is youth, Shava said. The outlet describes itself as producing "satirical comedy sensations." O'Donovan, a graduate of New York University, has called herself a manager for Magamba TV and a "media activist." Earlier this year, she presented a talk at a re:publica digital culture conference on "How Zimbabweans Rebel Online."

Zimbabwe Lawyers for Human Rights says it has represented nearly 200 people charged for allegedly insulting Mugabe, the world's oldest head of state, in recent years. Frustration is growing in the once-prosperous southern African nation as the economy collapses and the president, in power since 1980, is already running for next year's elections.

"This arrest marks the start of a sinister new chapter in the Zimbabwean government's clampdown on freedom of speech, and the new battleground is social media," said Amnesty International's deputy regional director, Muleya Mwananyanda. The statement said Zimbabwe authorities tracked tweets to O'Donovan's IP address.

"Concerned to hear of Martha O'Donovan's arrest and ongoing detention. #Mugabe must stop arresting journalists #FreeMartha," the New York-based Committee to Protect Journalists tweeted Friday.

News from © The Associated Press, 2017