Amnesty International has attacked the United Nations Security Council as "unfit for purpose" in its latest global report.
The human rights organisation accused the UN of letting down the Arab Spring by allowing Security Council members to veto resolutions that did not suit their commercial and military interests.
It also said the Irish Government's commitment to a Constitutional Convention was an opportunity for real human rights reform.
Speaking on the day of the Egyptian presidential election, Amnesty International Secretary-General Salil Shetty accused all the major powers of using the veto without a regard for the rights of ordinary people.
"Commercial interests, military interests of Russia and China, which have resulted in blocking the resolutions in favour of Syria, and the people of Syria - this form of using the veto has to come to an end," he said.
"The United States has also done similar sort of blocking to protect their own interests in Egypt, and the French in Tunisia.
"So there's a pattern of behaviour of the permanent members of the security council which makes it unfit for purpose."
Mr Shetty told a news conference in London that the courage of Arab Spring protesters contrasted with the failure of leadership at the UN.
"When there are big human rights violations, the Security Council should not be allowed to use its veto, and if they do, they have to give a very clear explanation of why they are doing that," he added.
Mr Shetty also criticised the new government in Libya, saying that in some cases the authorities were behaving almost as badly as Muammar Gaddafi's regime.
Executive Director of Amnesty in Ireland Colm O'Gorman said inaction over crimes against humanity in Syria and a failure to intervene in Sri Lanka left the UN Security Council looking redundant.
He added that the Irish Government must ensure the Constitutional Convention protects human rights that have long been ignored, such as health, housing and income.