The Zimbabwe pastor who fled to the US after launching the popular #ThisFlag protest movement faces up to 20 years in prison for organising protests against President Robert Mugabe in New York.

Evan Mawarire was arrested at Harare International Airport on his return home on Wednesday. He is yet to appear in court.

Mr Mawarire has been charged with subverting a constitutionally-elected government, an offence which carries up to 20 years in prison.

 Lawyer Harrison Nkomo said the charges arise partly from his role in organising anti-Mugabe protests during the UN general assembly in September last year.

Mr Mawarire is accused of organising Zimbabweans “to converge in New York to confront the president of Zimbabwe who was attending a United Nations seminar and order him to immediately resign from his position accusing him of destroying the country”, according to a police statement seen by the Associated Press and confirmed by his lawyers on Thursday.

He is also accused of using social media to incite “violent demonstrations” between August and last month.

He rallied Zimbabweans to protest against the government of Mr Mugabe, who turns 93 this month and is the world’s oldest head of state.

Police spokeswoman Charity Charamba on Wednesday said Mr Mawarire was picked up on an outstanding arrest warrant.

It was not immediately clear why Mr Mawarire had chosen to return home.

Some in Zimbabwe had criticised him for leaving the country amid the protests. At the time, he said he feared for the security of his family.

Before he left Zimbabwe, Mr Mawarire was detained and initially charged with inciting public violence before prosecutors changed the charges to attempting to overthrow a constitutionally-elected government.

A magistrate freed the pastor after ruling it was unconstitutional for prosecutors to bring the fresh charges in court.

Amnesty International’s deputy regional director for southern Africa Muleya Mwananyanda has called the latest charge against Mr Mawarire “absolutely ridiculous and a total sham”, saying it was meant to “punish him for speaking out about the declining human-rights situation”.

Mr Mugabe has said Mr Mawarire and others should leave Zimbabwe if they were unhappy with the country’s situation.