International human rights groups are urging the United Nations Human Rights Council to order a probe into alleged abuses committed during Sri Lanka's civil war.

Both London-based Amnesty International and New York-based Human Rights Watch on Tuesday called on the council to act on the recommendations of U.N. Secretary-General Ban Ki-moon.

The U.N. chief has sent a report to the Geneva-based U.N. Human Rights Council, which cites “credible evidence” of Sri Lankan troops and Tamil rebels committing possible war crimes in the final months of the conflict.

Sri Lanka's nearly three-decade civil war ended in May of 2009 with the military defeat of the Tamil Tiger rebels. The United Nations estimates that thousands of Tamil civilians were killed in the last phase of the fighting.

The U.N. Human Rights Council must agree to debate the report before it can give the secretary-general a mandate to launch an international investigation.

Amnesty International's Asia-Pacific Director Sam Zarifi said Tuesday that “now there can be no more excuses for inaction or delays.” Zarifi said it is time that the council act on the findings and hold accountable those responsible for “massive atrocities” in Sri Lanka.

Human Rights Watch's Asia Director Brad Adams said the U.N. Human Rights Council should feel compelled to act. Adams said anything less than a full international probe would be a “shameful abdication of responsibility.”

Meanwhile, U.S. Assistant Secretary of State Robert Blake continued his visit to Sri Lanka. On Tuesday, Blake traveled to former war zones in the country's north where he met with community leaders, students and local officials.

The day before, the U.S. diplomat discussed the status of Sri Lanka's own investigation with Sri Lankan President Mahinda Rajapaksa in Colombo.

Sri Lanka has rejected the U.N. report's findings and says it opposes an international probe. The government has appointed its own commission to investigate the civil war and is expected to publish its findings in mid-November.