China and Russia on Thursday blasted a US report that downgraded their countries for failing to make greater efforts to combat human trafficking, a move which could lead to sanctions.
"We believe that the US side should take an objective and impartial view of China's efforts (in fighting human trafficking) and stop making unilateral or arbitrary judgements of China," foreign ministry spokeswoman Hua Chunying said at a regular briefing in Beijing.
"The Chinese government always attaches great importance to fighting all crimes of trafficking," said.
In Moscow, a Russian official expressed his government's anger.
"As far as the application of unilateral sanctions against Russia is concerned... the very idea of raising this issue causes indignation," the foreign ministry's human rights envoy Konstantin Dolgov said in a statement.
The US State Department on Wednesday downgraded China, Russia and Uzbekistan to the bottom of a table on human trafficking.
The three nations had languished for years on the Tier 2 Watch List, having been granted past waivers amid promises to do better.
But under the terms of a 2008 law, they could no longer stay on the Tier 2 Watch List and either had to move up to Tier 2 or be downgraded to Tier 3 -- a move that could trigger cuts in non-humanitarian and non-trade US aid.
The report found that "trafficking is pronounced among China's internal migrant population" and "forced labour remains a problem, including in brick kilns, coal mines and factories".
China's one-child policy has resulted in "a skewed sex ratio of 118 boys to 100 girls in China, which served as a key source of demand for the trafficking of foreign women as brides for Chinese men and for forced prostitution".
Beijing had failed to "demonstrate significant efforts to comprehensively prohibit and punish all forms of trafficking", the report maintained.
Congressman Chris Smith, who has authored key legislation on trafficking, said China has become the "sex and labour trafficking capital of the world."
"Women and young girls have been -- and are today being -- reduced to commodities and coerced into prostitution," he added in a statement.
President Barack Obama will determine whether to enact any sanctions against the three nations in September.
The US estimates that about 27 million people remain enslaved around the world.