The United States has published a report revealing the massive scale of global human trafficking and blacklisting 19 countries for not doing enough to stamp out what it calls "a modern form of slavery".

Secretary of State Colin Powell, who unveiled the survey of practices in 89 countries, said it indicated the United States' resolve to stop an "appalling assault" on people around the world.

Worst offenders

Afghanistan Armenia Bahrain Belarus Bosnia Burma Cambodia Greece Indonesia Iran Kyrgyzstan Lebanon Qatar Russia Saudi Arabia Sudan Tajikistan Turkey United Arab Emirates

Legislation passed in 2000 calls for economic sanctions against countries who do not take action against traffickers or help their victims.

At least 700,000 and possibly as many as four million people are believed to be trafficked every year. Fifty thousand are brought into the United States alone.

"In this modern form of slavery... traffickers use threats, intimidation and violence to force victims to engage in sex acts or to labour under conditions comparable to slavery," the report says.

Many of the worst offenders are concentrated in the Gulf region.

Russia and other former Soviet republics are also among the 19 categorised in the report as "tier three" - failing to comply with minimum standards.

Another 52 countries fall into "tier two". They fail to comply with minimum standards but are considered to be making "significant efforts to bring themselves into compliance".

Eighteen mainly western European countries make the top grade of full compliance with the standards demanded in the 2000 legislation.

Mr Powell singled out South Korea, Israel and Romania for praise for their efforts in tackling trafficking over the past year.

Political priorities

But one of the lawmakers who introduced the legislation fears the US will shy away from criticising its allies and introducing the sanctions promised under the law.

We're talking about a situation of extreme exploitation where their women and young girls will be raped and abused in an horrific fashion

Congressman Chris Smith

"Whether they be friend or foe or any country in between, we've got to be very upfront... never whitewash human rights issues," said Congressman Chris Smith.

"We're talking about a situation of extreme exploitation where their women and young girls will be raped and abused in an horrific fashion.

"What person, what government official of any kind of calibre will allow that to happen to their own people?"

But the BBC's Jon Leyne says some of the worst offenders are also some of America's most necessary and sensitive allies at the moment - particularly in South Asia.

He says the issue of human trafficking is being eclipsed by more urgent priorities.