HARARE (Reuters) - A U.S. citizen was charged on Friday with attempting to overthrow the Zimbabwean government, which carries a sentence of up to 20 years in jail, after police earlier accused her of insulting 93-year-old President Robert Mugabe.

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Martha O’Donovan, who works for Magamba TV, which describes itself as Zimbabwe’s leading producer of political satire, was picked up in a dawn raid on her Harare home, her lawyer said.

O’Donovan, who denies both charges, was expected in court on Saturday, lawyer Obey Shava said.

Police spokeswoman Charity Charamba could not be reached for comment on the new, much more serious, charge.

O’Donovan was first charged with insulting and undermining the president, according to a police charge sheet, which accused her of last month calling Mugabe a “selfish and sick man” on Twitter, the first such arrest since the creation of a Ministry of Cyber Security last month.

That charge carries a maximum sentence of one year in jail, her lawyer said.

Shava said police then accused O’Donovan of setting up Magamba, being behind a “shadowy Twitter character” called @matigary and setting up another Twitter account @OpenParlyZw “for the sole purpose of overthrowing the government through unconstitutional means”.

The government has been particularly uneasy about social media after activists such as pastor Evan Mawararire and his #ThisFlag movement last year used social media to organize a stay-at-home demonstration, the biggest anti-government protest in a decade. A national election is due in 2018.

The police search warrant showed that central to its investigation was a post on O’Donovan’s Twitter feed referring to a “Goblin” whose wife and step-sons had imported a Rolls-Royce, an apparent reference to Mugabe, though he was not named.

In a statement to police seen by Reuters, O’Donovan said:

“I deny the allegations being leveled against me as baseless and malicious. That is all I wish to say.”

The U.S. embassy in Harare confirmed an American citizen had been arrested and said it was monitoring the situation closely.

Shava said his client had refused to sign a new document known as a “warned and cautioned statement” with the fresh charge. The document sets out the government’s case and signing it signals a suspect understands the charge.

She had signed the statement on the lesser charge.

Police seized her computers, cellphones and other electronic devices in the raid on her home.