Hong Kong pro-democracy activist Joshua Wong has been sentenced to 13.5 months in prison after pleading guilty to inciting and organizing an unauthorized protest outside the city's police headquarters last year, during months of unrest over a proposed extradition bill with China.

Two other activists, Agnes Chow and Ivan Lam, were sentenced to 10 months and seven months in prison respectively over the protest on June 21, 2019. Chow faced charges relating to inciting and taking part in the protest, while Lam was charged with inciting the protest.

The trio -- all former members of the disbanded political party Demosisto -- had been remanded in custody since Nov. 23, and were transferred from prison to court to hear their sentences. Hundreds of supporters turned out at the West Kowloon Magistrates Court Wednesday, as well as a small number of pro-China demonstrators.

In a letter he wrote in prison, published on his social media accounts prior to sentencing, Wong -- who faced up to three years in jail -- described how he had been placed in solitary confinement after an X-ray allegedly revealed "foreign objects" in his stomach. A prison service representative did not immediately respond to a request for comment about Wong's claims.

Wong's lawyer, Jonathan Man, said his client "was suffering during the period of solitary confinement," which he said ended last Thursday. Man added that while Lam was "okay," 23-year-old Chow was struggling in prison, as "it is the first time she was remanded and (she) was not used to the environment."

In a letter posted to Chow's social media accounts prior to Wednesday's sentencing, she wrote that she was having trouble sleeping and was feeling "under the weather." Chow added that she was "very worried" about the "high possibility" of her receiving a jail term. "I hope that everyone outside the prison walls are doing well," she said.

Wednesday's sentence marks the fourth time Wong has been jailed, and the longest sentence he has received, with previous stints in prison all lasting less than six months.

In the sentencing document, the court said that "deterrent sentences are warranted to safeguard public interests."

"Once again, the government has used the politically motivated charge of 'inciting others to protest' to prosecute people who have merely spoken out and protested peacefully," Amnesty International's Asia-Pacific regional director Yamini Mishra said in a statement.

"By targeting well-known activists from Hong Kong's largely leaderless protest movement, authorities are sending a warning to anyone who dares openly criticize the government that they could be next."

Mishra added that "even in protests where isolated acts of violence took place and public property was damaged, these should not be attributed to others or the organizers, or to the assembly in general."

POLITICAL PROSECUTIONS

Wednesday's sentencing was the latest related to the 2019 protests. About 2,000 people have faced charges such as rioting, illegal assembly and possession of weapons.

Wong himself faces other charges over a rally in October last year, and police have said investigations into the unrest are continuing.

Last month, a number of former pro-democracy lawmakers were arrested over protests staged in the city's legislature, while a reporter for public broadcaster RTHK was also detained.

The protests have largely stopped this year, due to COVID-19 social distancing restrictions and the national security law imposed on the city by Beijing in the summer. The law criminalizes secession, subversion and collusion with foreign forces, and carries with it strict prison terms.

It was used to bar Wong and a number of other candidates from standing for elections that were due to be held in September, but were postponed because of the coronavirus. Several of those disqualified were sitting lawmakers, who were subsequently ejected from the parliament by Beijing -- overruling constitutional precedent and bypassing Hong Kong's courts -- on November 11, sparking the mass resignation of the entire pro-democratic camp.

The move came the same week as the U.S. State Department sanctioned a number of top Chinese officials in Hong Kong for "threatening the peace, security, and autonomy" of the city, a move the local government described as "barbaric interference."

Other countries have also criticized China over the ongoing crackdown, with the European Council saying the move to disqualify opposition lawmakers constituted a "further severe blow" to freedom of opinion in the city and "significantly undermines Hong Kong's autonomy."

Some in Hong Kong have reacted to the worsening political system by emigrating -- or in the case of those facing prosecution, fleeing abroad.

This summer, a dozen Hong Kongers were arrested by the Chinese coast guard en route to Taiwan. All are now detained on the mainland and facing a raft of charges. A former independence activist, Tony Chung, was also arrested after allegedly attempting to claim asylum at the US consulate to Hong Kong, along with several others.

In his letter from prison, Wong urged the public to "continue to pay attention" to the 12 detained in China. Separately Tuesday, parliamentarians from 18 countries wrote to Hong Kong leader Carrie Lam to urge her to intervene on their behalf.

"In your role as Chief Executive, it is incumbent on you to intercede on behalf of these young people to ensure that they are guaranteed justice," the lawmakers wrote, expressing concern about a justice system "where imprisonment is essentially guaranteed, torture is common and forced confessions are frequently demanded of suspects."

"To continue to fail to do so would be a gross abdication of your responsibility to serve the people of Hong Kong and ensure their wellbeing and safety," the letter added.