Zimbabwean police arrested a US citizen on Friday for allegedly 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 stepson with his wife and first-lady Grace, Russell Goreraza, is thought 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 (190,000 euros) and have a top speed of 155 miles per hour -- 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.
"The US embassy has been in contact with the American who has been arrested and her counsel," an embassy spokesman told AFP. "We will continue to monitor the situation."
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 been convicted.
Two men were arrested separately on Friday after they allegedly said they would not vote for the ruling ZANU-PF party and comparing Mugabe to a dog.
The new cyber-security ministry is "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.