New photos emerged on Thursday of piles of dead bodies and execution-style killings allegedly taken during the final stages of Sri Lanka's civil war which ended in May last year.
Broadcaster Al-Jazeera said it had obtained the images from an unnamed source who said they had been taken by a member of Sri Lanka's military. It said it was unable to verify their authenticity.
The military onslaught against the Tamil Tiger rebel group has been dogged by allegations of war crimes, with Western nations and international rights groups pushing for a probe of possible violations by both sides.
Some of the disturbing photographs show bodies with twisted limbs piled on the back of a trailer, others show almost naked corpses, blindfolded and with hands bound behind their backs, lying in shallow graves.
Other similar photos and video footage have emerged in the past.
In January, UN human rights envoy Philip Alston concluded that video footage said to be of Sri Lankan troops executing unarmed Tamil Tiger rebels was authentic and urged Colombo to accept a war crimes probe.
"These photos provide compelling reasons for why there should be an independent international investigation into what happened," Yolanda Foster from rights group Amnesty International told Al-Jazeera.
Sri Lanka has set up its own probe, the Lessons Learnt and Reconciliation Commission (LLRC), which critics say lacks credibility and is intended to cover up atrocities.
The government, led by President Mahinda Rajapakse, rejects any accusation of war crimes and says no civilians were killed during the fighting.
New York-based Human Rights Watch, Amnesty International and Brussels-based International Crisis Group say up to 30,000 ethnic Tamil civilians perished in the final months of the conflict.
The Tigers fought for over 30 years for a separate state for the ethnic Tamil minority on the ethnic Sinhala-majority Indian Ocean island.