Respect for basic rights and liberties has declined in Sri Lanka in the four years since the government defeated the Tamil Tigers, Human Rights Watch said Monday.
This week marks the fourth anniversary of the brutal civil war's end.
Since the end of the 26-year-long civil war, the government of President Mahinda Rajapaksa has resisted taking meaningful steps to investigate and prosecute alleged war crimes by government forces and the LTTE, it said.
The government has also cracked down against the independent media and human rights activists and end ongoing abuses against suspected supporters of the vanquished Liberation Tigers of Tamil Eelam (LTTE).
"Government pledges to address the concerns of the ethnic Tamil population have gone unfulfilled," it said.
"Four years after Sri Lanka's horrific civil war ended, many Sri Lankans await justice for the victims of abuses, news of the 'disappeared,' and respect for their basic rights," said Brad Adams of Human Rights Watch.
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"Instead, the Rajapaksa government has rejected investigations, clamped down harder on the media, and persisted in wartime abuses such as torture."
Rajapaksa's assurances to UN Secretary-General Ban Ki-moon to investigate allegations of war crimes by all sides remain unmet, Human Rights Watch said.
The government disregarded the Ban's Panel of Experts report, which found that up to 40,000 civilians had died in the final months of the fighting, many from indiscriminate government shelling.
The government has similarly not implemented most of the accountability-related recommendations of its own Lessons Learnt and Reconciliation Commission.
Since 2009 the government has increasingly restricted fundamental liberties, imperiling Sri Lanka's democratic system, the rights body said.
Government officials have threatened, and unknown assailants have attacked members of the media, civil society and the political opposition, it said.
Activists who advocated for the 2012 Human Rights Council resolution were publicly denounced and threatened by officials.
The Rajapaksa government orchestrated parliament's impeachment of Chief Justice Shirani Bandaranayake in December 2012 after she had ruled against the government in a major case.
Publications, including electronic media, critical of the government have been subject to government censorship, and some have been forced to close down, it said.
The leading Tamil newspaper, Uthayan, has faced repeated physical attacks against its journalists and property.
Tamils with alleged links to the LTTE remain targets of arbitrary arrest and detention, and were at risk of torture and other ill-treatment, it said.
Sri Lankan security forces have used rape and other forms of sexual violence against alleged LTTE supporters.
The Prevention of Terrorism Act (PTA) continues to be used to detain individuals for long periods without charge or trial.
While there has been considerable economic development in Sri Lanka's war-torn north, much hardship remains for the predominantly Tamil population.
Many families seek to learn the fate of loved ones, some of whom are still detained as LTTE suspects without charge or trial.