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Roman Catholic bishops in Sri Lanka's former war zone have called for an international war crimes investigation into the country's civil war including whether government forces used cluster munitions and chemical weapons in densely populated areas.

Rev. Rayappu Joseph and Rev. Thomas Saundaranayagam made the request during a meeting with Stephen J. Rapp, an ambassador-at-large with the Office of Global Criminal Justice of the United States on Wednesday.

Joseph told reporters after the meeting in the northern town of Jaffna that civilians who survived a bloody final stage of a quarter-century civil war had reported that cluster munitions and chemical weapons were widely used.

The war ended in 2009 with the defeat of Tamil Tiger rebels.

The bishops asked that the investigations also look into allegations against the government of deliberate attacks on hospitals, places of worship and the blockade of food and medicine for the civilians trapped in the fighting as a war tactic, Joseph said.

Rapp is visiting Sri Lanka to discuss issues of alleged war crimes with government and other officials and has met religious leaders, ethnic Tamil politicians. He is scheduled to meet with government leaders before leaving the island nation on Saturday.

He has not commented on his meetings so far.

In 2012 a United Nations mine removal expert reported the presence of unexploded cluster munitions in the former war zone in northern Sri Lanka.

That same year a medical worker told The Associated Press that many of the thousands wounded in the government offensive had burns consistent with those caused by incendiary white phosphorus bombs.

U.N. officials first reported the use of cluster munitions in the conflict zone in February 2009, saying they appeared to hit in an area around a hospital.

The government however has continuously denied using cluster munitions or any banned weapon.

Cluster munitions are packed with small "bomblets" that scatter indiscriminately and often harm civilians. Those that fail to detonate often kill civilians long after fighting ends.

They are banned under an international treaty adopted by more than 60 nations that took effect in August 2010, after the Sri Lankan war.

Rapp's visit to Sri Lanka comes amid intense international pressure on the country to conduct its own investigations into the alleged war crimes committed by both sides.

The U.S. has sponsored two resolutions at the United Nations Human Rights Council urging a credible local investigation. The rights council is expected to review Sri Lanka's progress at its sessions in March.

U.N. rights chief Navi Pillay has said she will recommend that the council establish its own probe if Sri Lanka fails to show progress by March.

Meanwhile a group of Sri Lankan government supporters protested Thursday against Rapp's visit accusing America of ignoring its own human rights violations.

The banner-carrying protesters accused the U.S. of trying to victimize Sri Lanka for defeating the Tamil Tigers, who are designated as a terrorist organization by the U.S., European Union and others. They also said the U.S. was using a double standard by ignoring its own human rights violation.

A U.N report says as many as 40,000 ethnic Tamil civilians may have been killed in the last few months of the fighting, mostly by government troops.

Abuse allegations against the rebels include holding civilians as human shields, killing those who tried to flee their control and recruiting child soldiers.