Harare - Zimbabwean police arrested a US citizen on Friday for apparently tweeting that President Robert Mugabe is a "goblin whose wife and step-son bought a Rolls Royce", lawyers said.
Zimbabwe Lawyers for Human Rights (ZLHR) said officers detained Martha O'Donovan in a dawn raid at her home just weeks after Mugabe appointed a cyber security minister charged with policing social media.
Police confiscated her laptop and transferred O'Donovan, who works for Harare-based Magamba TV, to the city's central police station, the group added in its statement.
"The reported offensive and insulting tweet does not make any mention of the president's name," ZLHR said.
However Mugabe's step-son with his wife and first lady Grace, Russell Goreraza, is thought to be the only individual to have recently imported two Rolls-Royce vehicles into the country, local media reported.
The British-built cars, both Rolls-Royce Ghosts that sell for around $220,000 (over R3 million) and have a top speed of 250km/h, are marketed by the manufacturer as "more measured, more realistic" than the $300,000 Rolls-Royce Phantom.
Grace Mugabe's son is also reported to have purchased two Range Rover 4X4s, two Mercedes-Benz S-Class limousines and an Aston Martin, while Grace herself is also thought to have acquired a Rolls-Royce.
Police did not respond to calls for comment.
There have been several arrests in recent years for actions deemed to undermine the president, although no one has ever been convicted.
Two men were arrested separately on Friday after they allegedly said "I will not vote ZANU-PF and president Mugabe is like a dog," referring to the ruling party.
"Mugabe... created the cyber-security ministry as an attempt to clamp down on social media movements that pose a big threat to his regime ahead of the election," Bulawayo-based analyst Dumisani Mpofu previously told AFP.
Mugabe has already been named by ZANU-PF party as its presidential candidate for the 2018 poll.
Zimbabwe has an unemployment of more than 90 percent and rising levels of poverty.