As prison populations grow around the world, overcrowding creates conditions that amount to ill treatment or even torture, a UN official said Tuesday.

Juan Mendez, UN special rapporteur on torture, highlighted overpopulation in particular as he made a push before the UN General Assembly to revise the body's rules on the treatment of prisoners.

Growing incarceration rates, Mendez said, are "placing an enormous financial burden on states," with more than 10 million prisoners estimated worldwide.

"The global prison crisis has an adverse impact on conditions of detention," resulting in circumstances that Mendez said amounted "to ill-treatment or even torture."

In his report, Mendez said that the UN Standard Minimum Rules for the Treatment of Prisoners, adopted more than fifty years ago, have "significantly lagged behind recent developments in international human rights law."

Mendez took particular issue with a lack of an absolute prohibition of torture within the standards, and suggested better regulation of "the use of solitary confinement."

He also suggested that the rules extend to mental institutions and police stations, and that they contain guidelines for investigation on torture or inhuman treatment.