An international human rights group said Monday that respect for basic rights and liberties has declined in Sri Lanka in the four years since the government defeated separatist Tamil rebels to end a civil war.

Human Rights Watch said the Sri Lankan government has yet to follow through on its assurances to the United Nations to investigate allegations of war crimes by all sides.

"Many Sri Lankans await justice for the victims of abuses," said Brad Adams, the group's Asia director. He said the government has instead "rejected investigations, clamped down harder on the media and persisted in wartime abuses such as torture."

A government spokesman, Lakshman Hulugalla, declined to comment, saying he had not seen the Human Rights Watch statement. The government has rejected similar allegations in the past, saying they were false and biased.

Sri Lanka's quarter-century-long civil war ended in May 2009. The government held a military parade and war heroes memorial ceremony over the weekend to mark the victory over Tamil rebels who had fought for a separate state for their ethnic minority.

A U.N. investigation indicated the ethnic Sinhalese-dominated government might have killed as many as 40,000 Tamil civilians in the war's final months.

President Mahinda Rajapaksa's government initially denied that any civilian deaths occurred but later agreed to investigate instances of alleged abuses identified by its own war inquiry. A Sri Lankan commission report, released in December 2011, cleared government forces of wrongdoing.

The Sri Lanka government has argued that its own investigation should suffice, but international pressure has been growing for an independent investigation into possible war crimes.

In March, the U.N. Human Rights Council approved a U.S.-backed resolution calling on Sri Lanka to more thoroughly investigate alleged war crimes committed by both sides during the war.