Government security agents in South Sudan on Monday arrested at least two prominent activists who joined a call for a peaceful public uprising to seek political change, one of their colleagues said.
A coalition of civil society groups last week issued a declaration saying they have "had enough" after 10 years of independence marked by civil war, escalating insecurity, hunger and political instability.
Kuel Aguer Kuel, a former state governor, and renowned analyst Augustino Ting Mayai, were arrested in the capital Juba for signing the declaration, said Rajab Mohandis, another of the signatories.
The arrests came on the same day that hundreds of lawmakers were sworn in to a newly created national parliament, a key condition of a peace deal that ended South Sudan's brutal civil war.
The Sudd Institute, an independent think tank involved in the coalition, has also been shut down and its executive director Abraham Awolich is among other activists also being sought by the authorities, Mohandis told AFP.
Awolich said in a separate statement on Twitter that he was on the run after the Sudd Institute was stormed and its staff arrested over Friday's declaration by the People's Coalition for Civil Action (PCCA).
But he said he would not be bowed.
"Our people are rising up to fire the dictators and murderers and I am proud to stand with them. The time has come to bring down the failed yet dangerous regime."
The PCCA also remained defiant on Monday, saying in a statement it was intent on leading a non-violent "revolution" in the world's newest country and to seek "regime change".
It called for the resignation of both President Salva Kiir and his archfoe turned deputy Riek Machar, who remain uneasy bedfellows in the coalition government.
'Bankrupt political system'
The 2018 ceasefire and power-sharing deal between Kiir and Machar was just the latest accord signed by the two men whose rivalry ignited the conflict that cost the lives of almost 400,000 people.
Their truce still largely holds but it is being sorely tested, as politicians bicker over power and promises for peace go unmet.
South Sudan has struggled with war, famine and chronic political and economic crisis since celebrating its hard-fought independence from Sudan 10 years ago in July.
The PCCA described the current regime as "a bankrupt political system that has become so dangerous and has subjected our people to immense suffering, death and brought upon them abject poverty and destitution".
"The coalition is asking all the people of South Sudan to prepare for mass civil disobedience, strikes, sit-ins, protests and popular uprising to bring about change," it said.
Earlier Monday, 588 MPs -- a mix of delegates from the ruling party and former rebel factions who signed the truce -- took the oath of office in parliament in Juba.
The ceremony came nearly a year behind schedule and remains incomplete, with 62 MPs absent, some because of squabbles with the government over the power-sharing arrangement.