Nouakchott (AFP) - The Mauritanian parliament has adopted a new law as part of efforts to crack down on slavery, declaring it a "crime against humanity" and doubling prison terms for offenders.

Slavery was officially abolished in the west African country in 1981 and since 2007 those found guilty of involvement in the practice face up to 10 years in prison.

But according to several rights groups slavery still flourishes in the country, which has a long history of slavery.

The law voted late Wednesday said "slavery constitutes a crime against humanity" and criminalised "10 other forms of slavery" aside from conditions involving loss of freedom and work without pay.

Justice Minister Brahim Ould Daddah said maximum prison terms had now been doubled to 20 years.

Among the new situations criminalised are forced marriage for women and handing her over to another man, without her consent, after the death of her husband.

The new law also provides for legal help for victims and for the confiscation of assets of a convicted offender to compensate victims.

It said "credible" anti-slavery NGOs had the right to report cases and help victims.

Three anti-slavery activists will be judged on appeal on August 20 in the central town of Aleg.

They include two members from the Initiative for the Resurgence of the Abolitionist Movement in Mauritania, a prominent NGO.

They had been sentenced to two years in prison for "membership of an unrecognised organisation."