Malaysian police have detained a cartoonist and are investigating two lawmakers for sedition over tweets and a cartoon condemning the judiciary for dismissing opposition leader Anwar Ibrahim's final appeal against a sodomy conviction.

Anwar began a 5-year prison sentence Tuesday after the country's top court ruled there was overwhelming evidence showing that he sodomized a former male aide. The case was widely seen as politically motivated to eliminate any threats to the ruling coalition, whose popularity has been eroding after more than five decades of unquestioned dominance.

Police detained cartoonist Zulkiflee Anwar Alhaque, better known as Zunar, at his home late Tuesday over a series of tweets on Anwar's case. A cartoon he posted on Twitter showed Prime Minister Najib Razak as the judge in Anwar's case.

National police chief Khalid Abu Bakar also directed his men to investigate opposition lawmakers Nga Kor Ming and Rafizi Ramli for sedition. Nga tweeted it was time for the people to oppose a cruel regime, while Rafizi tweeted a cartoon of a judge wearing a white wig with the dollar sign on it.

The police moves were criticized by rights groups, with New York-based Human Rights Watch saying it was shameful that Malaysian authorities had turned peaceful criticism into a criminal act.

"Clearly it is designed to intimidate and instil fear in people on social media to go silent on their views. It is a further erosion of freedom of expression in Malaysia," said the group's Asia deputy director Phil Robertson.

Anwar has been the most vocal and visible symbol of the opposition's resurgence and is seen as the most potent political threat to Najib.

Anwar's second daughter, Nurul Nuha Anwar, on Wednesday launched a "March to Freedom" campaign, backed by her five siblings. Eldest sister Nurul Izzah is already a lawmaker.

Nuha said the family was devastated and outraged over the "malicious persecution" of Anwar that led to his jailing again.

The new campaign will be a struggle to free Anwar from unjust incarceration and give voice to Malaysians who have suffered injustice, she said.

"These seventeen years have been an emotional roller coaster. We do not know how long this struggle will continue but we will be with our father till the end," said Nuha, 31. Details of the campaign will be announced later.

Anwar was accused of sodomizing Saiful Bukhari Azlan, then 23, who was working as a lowly aide in the opposition campaign office in 2008.

Homosexuality is a crime in Malaysia punishable by up to 20 years in prison and by whipping, although prosecutions are rare.

Anwar was acquitted by the High Court in 2012 but the Appeals Court overturned the acquittal in March last year and sentenced him to five years in prison. Anwar appealed in Federal Court, but lost the battle Tuesday.

The Federal Court in its ruling said Anwar's allegation that the case was a political conspiracy was unsubstantiated.

Addressing the judges from the dock after the verdict, Anwar said the charge was a "fabrication coming from a political conspiracy to stop my political career."

"You have become partners in crime in the murder of judicial independence," he said, prompting the five judges to walk out of the room.

Anwar vowed that he "will not be silenced. I will fight on for freedom and justice. I will never surrender."

Shortly after the verdict, the Prime Minister's Office said the judiciary is independent and that Anwar's case has gone through an exhaustive legal process.

The U.S., U.K., Australia and the E.U. expressed concern over Anwar's jailing, with the White House saying the trial raised serious concerns about rule of law and the fairness of the judicial system in Malaysia.

Anwar previously was imprisoned for six years after being ousted as deputy prime minister in 1998 on earlier charges of sodomizing his former family driver and abusing his power. He was freed in 2004 after Malaysia's top court quashed that sodomy conviction. That case was also widely seen as politically motivated, as it came at a time when he was locked in a power struggle with then Prime Minister Mahathir Mohamad.

Anwar led his alliance to unprecedented gains in 2008 elections and made further inroads in 2013 polls. Najib's National Front coalition won with a slimmer majority and lost the popular vote to the opposition.