The top U.N. human rights official has arrived in Sri Lanka on a four-day visit aimed at reviewing the measures taken by the island-nation to investigate alleged atrocities committed during the long civil war that left tens of thousands dead.

The visit by Zeid Raad al-Hussein follows last year's resolution at the U.N. human rights body that required foreign judges to assist Sri Lanka in the investigation.

Sri Lanka's civil war ended in 2009, after the government forces crushed the separatist Tamil Tiger rebels.  Both sides were accused of committing grave human rights abuses such as killing civilians and recruiting child soldiers.

Zeid will meet government officials, civil activists and victims of rights violations.