Amnesty International has launched a global anti-torture campaign, calling for an end to the practice which it acknowledges is becoming less frequent.

Amnesty singled out five countries where torture is considered a particular problem and where it believes its campaign can have the most impact.

The countries identified for the campaign are Morocco and Western Sahara, Nigeria, Mexico, the Philippines and Uzbekistan.

Amnesty International has said perpetrators of torture enjoy almost "total impunity" in Morocco and Western Sahara.

It said that, despite being explicitly criminalised since 2006 and prohibited by the new 2011 constitution, torture continues in Morocco, with perpetrators enjoying "virtual total impunity" and judges rarely investigating reports of torture.

"The resulting climate of impunity cancels out the dissuasive power of Morocco's anti-torture legislation," Amnesty said.

The government rejected the charges, insisting that judicial procedures had been strengthened, that the justice ministry was ready to investigate any claims of torture and that new reforms were planned that would see police interrogations recorded.

"Morocco has adopted a voluntary and systematic policy aiming to promote and protect human rights in all regions of the kingdom without distinction," government spokesman Mustapha Khalfi said.

Amnesty highlighted key steps Morocco has taken to confront concerns about the ill-treatment of detainees by the security forces, notably setting up an Equity and Reconciliation Commission in 2003 to investigate atrocities committed under the late King Hassan II.

The government's decision in March to end the trial of civilians in military tribunals was also seen as strengthening the rule of law and progress towards halting convictions based on confessions obtained through torture.

But Amnesty cited three specific cases in which detainees signed "confessions" after being subjected to torture or other ill-treatment in police custody.

One was Ali Aarass, a Belgian-Moroccan extradited from Spain in 2010. He was jailed for 12 years on "terrorism" charges, despite documentation that he was repeatedly tortured and claims that his "confession," the main evidence against him, was obtained through torture.

In Western Sahara, one of six Sahrawis arrested during a pro-independence demonstration last year claims he was threatened with rape and forced to sign a "confession" that he was prevented from reading.

He and his co-defendants, who were bailed in October after five months in pre-trial detention, risk up to 10 years in prison, accused of violence against public officials and participating in an armed gathering.

Amnesty called on Morocco to "end the climate of impunity" by prosecuting all those against whom there is sufficient evidence.

It also urged the authorities not to use confessions obtained through torture in any proceedings, to end secret detentions and to ensure that detainees have access to a lawyer, notably during interrogation.