Algeria and Guinea were the other additions to the blacklist of the State Department's annual "Trafficking in Persons Report," which analyzed efforts in about 164 countries to combat trafficking for forced labor, prostitution, military service and other purposes.

The seven countries, all of whom were on a special watch list last year, join Myanmar, Cuba, Iran, North Korea, Saudi Arabia, Sudan, Syria, Uzbekistan and Venezuela in the dreaded "Tier 3" list as the worst offenders of human trafficking.

Being on the blacklist, they could face sanctions, including the withholding by the United States of non-humanitarian, non-trade related foreign aid.

Countries that receive no such foreign assistance would be subject to withholding of funding for participation by government officials in educational and cultural exchange programs.

Launching the 236-page report, Secretary of State Condoleezza Rice cited "disturbing evidence" that prosecution of human trafficking cases had levelled off across the globe.

In countries with major human trafficking problems, "only a couple" of traffickers were brought to justice, she said. "This cannot and must not be tolerated."

"Human traffickers prey on the most vulnerable members of society -- most often innocent women and children, exploiting and abusing them and profiting from their suffering," she said.

US government research shows 800,000 people are trafficked across national borders, about 80 percent of them women and girls and up to half minors, the State Department said.

The majority of transnational victims are females trafficked into commercial sexual exploitation, it said.

The wealthy Middle East nations added to the blacklist this year were largely accused of mistreating foreign workers, which they heavily rely on.

"It is especially disappointing that so many wealthy countries in the Near East that aren't lacking resources to make significant progress are on Tier 3, for example Saudi Arabia for the third consecutive year," said Mark Lagon, Rice's senior advisor on the human trafficking problem.

He said weak foreign workers' sponsorship laws in these countries made the guests "vulnerable" to abuse in both private homes and worksites. Some of the victims who reported their abuse were instead "held hostage," sometimes for years, in police centers.

A key trend in trafficking cases, especially those linked to labor and sexual exploitation, is illegal debt, investigations show.

It is "increasingly used to keep people in servitude," Lagon said. "This debt is used by traffickers as an instrument of coercion."

He dismissed suggestions that politics played a part in categoriz-ingnations facing trafficking problems, citing Zimbabwe, which has a blemished human rights record, as an example.