Hong Kong, Aug 30 (IANS): Three prominent Hong Kong democracy activists, including Joshua Wong who was one of the main leaders of the Umbrella Revolution in 2014, were arrested on Friday for their involvement in an unlawful assembly, the police said.

Wong, pro-independence activist Agnes Chow and campaigner Andy Chan are seen as key figureheads of anti-government movements in Hong Kong over recent years. Their arrests come on the eve of a proposed mass protest that has been banned by police.

Wong was arrested on three charges of organizing, inciting and taking part in an illegal assembly during a siege of police headquarters on June 21, when demonstrators demanded a complete withdrawal of a now-shelved extradition bill and an exoneration of those arrested in previous clashes.

Chow was detained on charges of inciting and taking part in the same assembly, the South China Morning Post reported. They were later released on bail, according to the BBC.

Independence campaigner Chan was arrested on Thursday night on suspicion of rioting and assaulting a police officer during a protest. He was stopped from boarding a plane leaving for Tokyo at Hong Kong airport.

These activists are among 900 people arrested since protests began in June.

Wong -- who served time in jail for his role in the 2014 Occupy movement -- was detained on his way to a metro station, while Chow was arrested at her home in Tai Po. They are leaders of the pro-democracy outfit Demosisto, which has been campaigning for democratic self-determination in Hong Kong. 

A third member of the party, Ivan Lam Long-yin, was charged with inciting others to take part in an unauthorized assembly. He was said to be out of town and did not show up at court.

Sha Tin District Council member Rick Hui Yui-yu was also arrested on suspicion of obstructing officers in the execution of their duty in relation to the July 14 clashes at a shopping mall in the area, the police said.

In a Facebook post, Demosisto called the arrests a "political operation" and warned that they could lead to "a deadly situation that is more difficult to resolve".

August 31 marks the fifth anniversary of Beijing's stringent "831 Decision" on Hong Kong's democratic reforms. 
Protesters had planned to launch another mass demonstration before they were banned by police.

The arrests come after the police earlier this week rejected the Civil Human Rights Front's plan to march from Central to Beijing's liaison office in Sai Ying Pun on Saturday. 

The Front is behind the biggest marches held in Hong Kong since the eruption of the political crisis in early June, sparked by the now-abandoned extradition bill, which would have allowed criminal suspects to be sent back to mainland China.