Pressure is building on the Sri Lankan government to investigate war crimes allegedly committed by its military against captured Tamil rebels two years ago.

Video footage purporting to show Sri Lankan army soldiers executing surrendering Tamils forms the basis of a UK Channel 4 documentary shown to the UN's Human Rights Council last weekend.

Sri Lankan government officials deny the video is authentic, or that there have been any war crimes committed by their military.

Sri Lankan Tamil activists have joined human rights groups in calling for the International Criminal Court (ICC) in The Hague to start an investigation into alleged war crimes. But this process can only begin, according to the office of UN Secreatry General Ban Ki Moon, when the "host country [Sri Lanka] consents, or [following] a decision from [UN] member states through an appropriate intergovernmental forum".

American inconsistency

One appropriate forum could be the very UN Human Rights Council which, at an informal meeting, saw the tape at the weekend. But before the subject can even make it onto the Council’s agenda, a member state needs to make a good case for its inclusion.

That prospect has been undermined by the United States' departments of State and Defence, which have contradicting each other on the issue - the former saying it was "deeply concerned" by alleged Sri Lankan war crimes, the latter questioning the credibility of those accusations.

Long and winding road

If the issue ever did get through the UN Human Rights Council, it would still need to get past the veto-wielding five permanent member states of the UN Security Council before being referral to the ICC and a formal investigation begun.

The allegations of atrocities on both sides are credible – the number of western nations expressing grave concern at the evidence make them so.

What presents a serious problem according to Sri Lankan Groundviews journalist Sanjana Hattotuwa is a lack of credibility in the government’s approach to investigating war crimes.

“When a shorter version of the Channel 4 video was shown in 2009… the government appointed a four-member panel to look into it, two of whom were from the army. Now you just can’t do that because part of the allegations is against the army itself.”

For Hattotuwa, failure to address the questions now being raised more loudly by the UN are vital to Tamils and Sinhalese alike.

"Justice needs to be seen to be done as much as it is done… and if we do not address this it could lead to discontent, and years down the line, another war. And none of us wants that".