Sri Lanka's President Mahinda Rajapaksa declared on Tuesday that he will prohibit United Nations investigators from entering the country as part of an inquiry into alleged war crimes committed in the waning weeks of its civil war.

"We will not allow them into the country," Rajapaksa told reporters, arguing that Sri Lanka's own investigation, which was set up in 2010, made the UN inquiry redundant. "We are saying that we do not accept it. We are against it."

Observers such as Amnesty International have criticized Sri Lanka's Lessons Learnt and Reconciliation Commission as fundamentally flawed and toothless, however, underscoring the need for a credible international investigation.

Last September, Pillay's office said it had "detected no new or comprehensive effort to independently or credibly investigate the allegations which have been of concern to the Human Rights Council."

"The government has never shown any real interest or commitment to accountability for the crimes, so in that sense, the decision [to bar UN investigators] is no surprise," John Sifton, Asia advocacy director at Human Rights Watch, told VICE News. "On some level they're operating in an atmosphere of self-delusion where they don't actually believe that major human rights abuses were committed. They think that everything they did was excusable and justifiable, and that nothing happened."

Sources cited by the UN estimate that as many as 40,000 Tamil civilians were killed, mostly by government forces, in the period just before Rajapaksa declared victory in May 2009. Many are believed to have perished in hospitals and in areas within no-fire zones agreed upon with the UN.

The deaths culminated a brutal 26-year war between the Sinhalese Buddhist government and army and Tamil Tiger separatists seeking to create an independent state for the country's historically marginalized Tamil minority, which is predominantly Hindu.

The conflict saw the killing in 1991 of former Indian Prime Minister Rajiv Gandhi by a Tamil suicide bomber, a brazen Tamil Tiger attack on Colombo's International Airport in 2001, and severe oppression by the Sri Lankan government of Tamil communities.

In March, the UN Human Rights Council voted to open an inquiry into actions that took place between 2002 and 2011. The investigation is expected to focus in large part on later events in the country's northwest, including the actions of Tamil Tiger rebels who are alleged to have forced civilians to travel with them as they retreated under a barrage of government shelling. Much of the Tiger leadership, including its founder Velupillai Prabhakaran, perished in 2009.

China holds large investments in Sri Lanka and voted against the inquiry, along with Russia and ten other countries, when the UN Human Rights Council adopted the resolution. Unlike the Security Council, no member state on the Human Rights Council has veto power. A total of 23 members of the Council, including the US and the UK, voted in favor of the investigation, while 12 abstained.

The inquiry, which opened in July, is not expected to deliver its report until next year.

The Sri Lankan government has repeatedly claimed that UN High Commissioner for Human Rights Navi Pillay, a South African jurist of Indian Tamil descent, is biased against it, accusing her of "prejudice and lack of objectivity." She will leave her post at the end of August, replaced by Jordan's representative to the UN, Prince Zeid bin Ra'ad.

Pillay recently said that the UN's inquiry can proceed without investigators actually setting foot in the country, pointing to investigations of Syria and North Korea that faced similar obstacles. Witnesses can be interviewed via Skype and teleconferences, and sites can be scrutinized using satellite imagery. Still, the lack of access will make the UN's work difficult.

"We hope that the government of Sri Lanka will review its decision not to engage with the investigation," Ravina Shamdasani, a spokesperson for Pillay's office, told VICE News. "The government will continue to be invited to present information to the investigation."

Despite pressure from Western countries, including many with large Sri Lankan Tamil diaspora communities, there appears to be little they are able to do to assist the inquiry.

"We will continue to urge the Sri Lankan government to co-operate with the resolution in full," a spokesperson for the UK's mission to the UN told VICE News.

Since the end of the war, Rajapaksa has made little effort to reconcile with the still besieged northern Tamil community, allowing Sinhalese settlers to colonize the region and watching as radical Buddhist monks foment hatred of minorities. He has dismissed Tamil political parties as remnants of the Tigers.

Sri Lankan officials charge that the UN investigation threatens to imperil the development of the island, which they say depends on them being able to resolve the war's legacy on their own.

The UN inquiry "will only strengthen the hand of those who are seeking to destruct the progress that we are making towards economic success and reconciliation," Palitha Kohona, Sri Lanka's ambassador to the UN, told VICE News, referring to vestiges of the Tigers.

"Within the country itself, there is no demand for an inquiry of this nature," Kohona said. "The majority of the people in the country would never support such an inquiry."

Predominantly Buddhist Sinhalese constitute about three-quarters of the country's population. The investigation would look in large part at crimes whose victims were mostly members of Sri Lanka's historical Tamil community, who make up roughly 11 percent of the population.

Sifton explained that the posturing of Rajapaksa's government serves to increase their standing with the Sinhalese electorate.

"You rack up domestic points by xenophobically suggesting that your country is under an international conspiracy to undermine its sovereignty," he said.

Kohona, however, insists Sri Lanka is being unfairly singled out, and called attention to the protests in Ferguson Missouri as an example of uneven treatment.

"How many inquiries are there to look into what's happening in Iraq, in Syria, Afghanistan, in the United States?" asked the ambassador. "The rioting taking place in Missouri at the moment — dozens of people have been arrested. Have there been international inquiries? No. So why little Sri Lanka?"

Visvanathan Rudrakumaran, a former legal advisor to Prabhakaran who is now the prime minister of the self-proclaimed Sri Lankan Tamil government-in-exile, also brought up Ferguson in a conversation with VICE News.

"The Secretary General has called Gaza a moral outrage and made a statement on the Missouri teenager also," said Rudrakumaran, who practices immigration law in New York City. "In light of this, we are asking him to publicly sanction the Sri Lankan government for not allowing investigation into these crimes."

Follow Samuel Oakford on Twitter: @samueloakford