Harare, Zimbabwe(CNN) Zimbabwe police have arrested the pastor who fled the country last year after leading protests against President Robert Mugabe's government.
Pastor Evan Mawarire's #ThisFlag protest movement gained momentum among Zimbabweans on social media last year after he called on Mugabe's government to address a failing economy and to respect human rights.
His attorney, Harrison Nkomo of Zimbabwe Lawyers for Human Rights, told CNN his client was detained upon arrival in Harare on Wednesday and charged with "subverting a constitutionally elected government."
He added that Mawarire was acquitted of the same charges last year and that they would fight these charges again.
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Mawarire spent six months in self-imposed exile in the United States after first fleeing to South Africa following his arrest.
Human rights group Amnesty International Thursday called for his immediate release.
"The authorities must immediately and unconditionally release Pastor Evan Mawarire, as he is a prisoner of conscience imprisoned solely for the peaceful exercise of his rights," Amnesty deputy regional director for South Africa Muleya Mwananyanda said in a statement.
"It is designed to make him stop his human rights activism and to punish him for speaking out about the declining human rights situation in Zimbabwe," Muleya added.
Mawarire told CNN's David McKenzie last August he was afraid to go back home.
"Because when you look at first and foremost the charges that the State then brought against me... you start to see that the agenda may be a little deeper than at least I expected. So the fear of going back home is there because I fear a re-arrest, and... I fear that somebody may attack me or somebody may want to bring harm to myself or my family," he said.
Mawarire first became noticed in April of 2016 when he draped himself in a Zimbabwean flag and railed against the government in an online video. In the process, he started a movement, #ThisFlag, hoping to end corruption and bring transparency and accountability to the government and its long-running President.
Mawarire was detained July 12 for "inciting public violence," -- a count that was subsequently amended to a much more serious charge of subversion -- but was released the next day under immense public pressure, when the court ruled the police had violated his rights.
In the weeks after the pastor's first video, Zimbabwe saw rare anti-government street protests and widespread strikes in the form of so-called "stay-away days."
Mugabe called the pastor a fake, and said he was "foreign sponsored."