Asylum seekers were subjected to sexual abuse and assault by immigration officials paid by Australia, while living on the remote Pacific island of Nauru, according to a series of leaked documents.

The documents, obtained by the Guardian, lift the lid on the distressing conditions for asylum seekers hoping to settle in Australia. Nauru has long been known for its harsh conditions, at the hands of authorities.

Last week Human Rights Watch and Amnesty International published reports into the remote Pacific island – the third smallest independent country in the world, after Vatican City and Monaco – which has accepted aid money from Australia, in return for housing asylum-seeker camps.

They claim that Australia turns a blind eye to the abuse, to discourage other refugees from making asylum claims.

"Few other countries go to such lengths to deliberately inflict suffering on people seeking safety and freedom," said Anna Neistat, senior director for research at Amnesty International, who conducted the investigation together with a researcher from Human Rights Watch.

On Tuesday the Guardian published an analysis of more than 2,000 leaked incident reports, from May 2013 to October 2015, which total more than 8,000 pages.

As of the end of June 442 people – 338 men, 55 women and 49 children – were being held in the Nauru regional processing centre, in the last official count.