Harare - A 25-year-old American journalist charged with attempting to overthrow Zimbabwe's President Robert Mugabe, on account of an alleged tweet that described the ageing leader as "selfish and sick", was remanded in custody on Saturday after denying the accusations.Martha O'Donovan, who appeared in court in the capital Harare, was charged with subversion as well as undermining or insulting Mugabe, now 93.The arrest of O'Donovan and the seizure of her laptop in a dawn raid at her apartment on Friday, came just weeks after the government appointed a cyber security minister tasked with policing social media.Prosecutors said that on October 11, O'Donovan posted a message on Twitter under username "@matigary" which said: "We are being led by a selfish and sick man". The tweet was illustrated with a photo showing the Zimbabwean president with a catheter device."Our client is vehemently denying both charges," her lawyer Obey Shava told AFP, adding that O'Donovan would apply for bail on Monday at the High Court.O'Donovan works for Harare-based Magamba TV, which describes itself as a leading producer of cutting edge political satire and comedy. Its content goes out on YouTube.Human rights lawyers on Friday had said the arrest was linked to a retweet which did not mention Mugabe by name but referred to a "goblin whose wife and step-son bought a Rolls-Royce".Mugabe's stepson with his wife and first-lady Grace, is thought to have recently imported two British-built Rolls-Royce vehicles, according to local media reports.But a charge sheet read in court on Saturday referred to the different post on Twitter that specifically mentioned Mugabe.The US embassy said on Friday that it had been in contact with O'Donovan and her legal counsel.The cyber-security ministry was created in Mugabe's latest cabinet reshuffle last month which also saw his deputy Emmerson Mnangagwa being stripped of his justice portfolio.The new ministry is seen by rights groups as an attempt to clamp down on social media in the run up to next year's election."Some use the internet to fight us and implement what they say is regime change," Mugabe said on Saturday while commissioning a community information centre in the southern city of Bulawayo while O'Donovan was appearing in court.Mugabe has already been named by his ruling Zanu-PF party as its presidential candidate for the 2018 poll.