The New York based rights group, Human Rights Watch, urged Sri Lanka's new president to "advance a reform agenda to address past and ongoing human rights problems in the country" and stressed the need for accountability for violations of international law during the armed conflict in a letter sent to the president on Thursday.

Stating that the government had undertaken important new initiatives, HRW said in a statement accompanying the letter, "however many important human rights concerns still need to be addressed".

"Among them are the use of torture by police, the protection of minority communities, the independence of government oversight committees, and the repealing of the Prevention of Terrorism Act (PTA). Holding accountable those responsible on both sides for violations of international law during Sri Lanka’s long civil war is crucial for the country’s future," the rights group added in a statement on Thursday.

"The Sri Lankan police routinely torture and ill-treat criminal suspects taken into custody.  The government should act to eliminate the use of torture against detainees and improve redress mechanisms for victims."

"During the Mahinda Rajapaksa government, Sri Lanka’s minority communities increasingly came under threats and violence instigated by ultra-nationalist Buddhist groups. While the new president in several speeches has acknowledged the government’s failure to act on behalf of these minority groups, more needs to be done to alleviate their concerns. The government should fully investigate and appropriately prosecute members of sectarian groups for inciting communal violence, as well as police who failed to stop such crimes."

"The number of people arbitrarily detained under the Prevention of Terrorism Act is unknown, and many of their families are unaware of their fate or whereabouts. In addition to releasing or charging those detained, the government should promptly act to repeal the law, which has long underpinned widespread human rights violations, particularly against ethnic Tamils."

"On accountability for wartime abuses, the decision of the United Nations to postpone the release of its investigation into violations of international law in Sri Lanka until September 2015 provides the government an opportunity to put into place an effective mechanism with a significant international component. Previous government accountability mechanisms have been impaired by harassment, threats and violence against witnesses and judges. The best way to address this problem would be to create a combined international and domestic court similar to the successful hybrid courts in Sierra Leone and Bosnia-Herzegovina."

HRW's Asia director Brad Adams added: “Creating a predominant international presence in a special Sri Lankan court would reduce the scope for interference against national judges and prosecutors."

“A strong hybrid court would lend credibility and independence to the proceedings that purely domestic proceedings may lack.”

See letter here.

Final recommendations by HRW to Mr Sirisena reproduced below:

• Act to eliminate the use of torture and other ill-treatment by police against criminal suspects.  Improve redress mechanisms for victims of torture.

• Investigate and appropriately prosecute those responsible for incitement of violence against religious minority communities and law enforcement officials who fail to stop it. Send an unequivocal message that communal violence will not be tolerated.

• Investigate and appropriately prosecute those who have committed threats and attacks against members of civil society and the media.

• Repeal the Prevention of Terrorism Act. Ensure that those detained under the PTA are promptly released unless charged with a credible offense. Take all necessary steps to end the use of torture, including by eliminating all unofficial detention centers and prosecuting those responsible.

• Increase consultations with civil society organizations on a broad range of human rights issues to consolidate and expand upon recent improvements.

• Seek visits and assistance from United Nations technical and expert bodies to address human rights concerns.

• Make public past reports of Sri Lanka’s various commissions of inquiry; ensure the August 2015 release of the pending Disappearances Commission report.

• End the practice of returning refugees and asylum seekers to places where they have a reasonable fear of persecution.

• Establish a special hybrid international-domestic court to prosecute those on both sides responsible for serious violations of international law.

• Put in place a victim and witness protection program that complies with international best practice.