Eranga Jayawardena / AP Sri Lanka's President Mahinda Rajapaksa, right, listens to Army Commander Lt. Gen. Daya Ratnayake during celebrations of Sri Lanka's 66th Independence Day northeast of Colombo, Sri Lanka, Feb. 4, 2014.

Sri Lanka’s President Mahinda Rajapaksa remained defiant in the face of intensifying calls for an independent war crimes investigation this week. United Nations High Commissioner for Human Rights Navi Pillay recommended in a Feb. 24 report that an independent, international inquiry be launched into alleged human rights violations in 2009, during the final phase of Sri Lanka’s long and bloody civil war against ethnic Tamil separatists.

Speaking to TIME and a handful of other news outlets in Colombo on Friday, Rajapaksa insisted “no one knows why” the West is pushing for the investigation. “We are convinced there are various hidden agendas,” said Rajapaksa, who has been if office since 2005. He has long insisted his administration is being bullied by western powers over how it has handled its post-war reconstruction and reconciliation efforts.

“It is like Cassius Clay fighting a school boy,” the president said. But, he added, “they can’t knock us down.”

Pillay’s report says that Rajapaksa’s government has “failed to ensure independent and credible investigations” into human rights violations and possible war crimes, despite the fact that new evidence continues to emerge about the last stages of the war. She also raised concerns over “the continuing trend of attacks on freedom of expression [in Sri Lanka], peaceful assembly and association… and continued militarization.”

The scathing report comes a few months after Colombo hosted the biennial meeting of Commonwealth nations, an event that Canada’s Prime Minister Stephen Harper boycotted and that Indian Prime Minister Manmohan Singh declined to attend. U.K. Prime Minister David Cameron did attend the summit, but used the occasion to visit the island’s war-ravaged north in what many considered a rebuke to his host. On Feb. 28, British Foreign Office Minister Hugo Swire released a statement welcoming Pillay’s report. Swire said his office shares “her concerns about the human rights situation in Sri Lanka and the lack of progress on accountability” and “strongly support[s] her call for an international investigation.”

The United Nations Human Rights Council has passed two U.S.-backed resolutions calling for the government to investigate war crimes allegedly committed by both the military and the Liberation Tigers of Tamil Eelam (LTTE) during the last phase of the nation’s decades-long civil war. Washington is expected to support a third, tougher resolution next month at a meeting of the UN Human Rights Council that would back Pillay’s recommendation.

On Friday, Gamini Lakshman Peiris, Sri Lanka’s Foreign Minister, reiterated Colombo’s rejection of any such kind of “international investigation,” and said there is no justification for the “disproportionate” attention that the global human rights community is putting on Sri Lanka.