China executed more people than any other country in the world last year by putting at least 470 people to death, but the number of executions in the country actually fell compared to the year before, Amnesty International said.

In its annual report on worldwide executions, the human rights group said Tuesday that Iran remains the country with the second highest number of executions, and that the number had nearly doubled from the year before. The 377 inmates included a man stoned to death for committing adultery.

The United States was fifth in the rankings with 42 executions, reflecting a drop in the number of people put to death during the year. That was the lowest number of executions in the United States in about 15 years, Amnesty officials said. However, lethal injection executions have been on hold nationally while the U.S. Supreme Court considers a challenge in a case from Kentucky.

Amnesty analysts said China reformed the way capital cases are handled early in 2007, leading to a substantial reduction in executions. But they cautioned that the actual number of people put to death in China in 2007 is undoubtedly higher than the figure of 470 executions that could be confirmed — and they warned that the drop may be temporary.

"We do actually believe there has been a reduction in number of executions," said Piers Bannister, a death penalty researcher at Amnesty. "But how permanent and how significant that reduction is we don't know because it's a state secret."

One reason the number of people reported executed in China fell may be the reintroduction in January 2007 of a review by its top court of all capital cases, Amnesty said. The legislation is aimed at weeding out unfair convictions and reserving the death penalty for only the most severe cases.

But analysts are concerned the number could rise again because of a backlog in executions due to the extra set of judicial reviews. This makes them cautious about judging the significance of the halving of the number of people killed by the Chinese state.

The Chinese Foreign Ministry in Beijing did not respond to requests for comment on the findings in the Amnesty report. The ministry has said in the past that Amnesty is "biased and hostile toward China."

Rosemary Foot, professor of international relations at St. Antony's College at Oxford University, said Chinese leaders would be embarrassed by the report showing China again leads the world in executions.

"Obviously, it's an image issue," she said. "It's always going to be the phrase that's on everyone's lips, the highest number." She said the report would hurt China's reputation outside its borders but would have little impact inside the country.

Foot said it was impossible to obtain reliable figures about executions in China because of the secrecy surrounding the process. "The caveat is, there's not openness about levels of execution. We don't actually know what the real figure is."

There are more than 60 offenses in China that are punishable by death, Bannister said. They include drug trafficking, embezzlement and other financial offenses.

In its report, Amnesty also "expressed deep concern" that many more people were killed secretly in countries such as Mongolia, Vietnam and Malaysia.

It urged countries to heed a United Nations resolution in December 2007 calling for the open and transparent use of the death penalty as a step toward abolishing it altogether. Amnesty also criticized other countries for executing people for offenses not ordinarily considered criminal, or after unfair procedures.

It cited the case of an Egyptian beheaded in Saudi Arabia for sorcery. Amnesty also reported that three countries — Iran, Yemen, and Saudi Arabia — put people under the age of 18 to death.

The youngest was a 13-year-old executed in Iran in April.

Amnesty said the number of executions in China fell from 1010 in 2006 to 477 last year. But its report cites other groups that claim last year's number was much higher.

For example, research by the U.S.-based Dui Hua Foundation, which campaigns on behalf of political prisoners and researches conditions in Chinese prisons, indicates about 6,000 people were executed in 2007. The group's data are based on figures obtained from local officials.

Death penalty figures are treated as a state secret in China. The country's top judge said last month that only "extremely vile criminals" were executed last year.

The death penalty is believed to have popular support in China, but the reform begun last year shows the government is trying to change a system that often put people to death just a few weeks after conviction for crimes ranging from murder to corruption.

Bannister said Amnesty's report "really is a challenge to China to end the secrecy," especially as it prepares to host the summer Olympics in Beijing in August.

China also topped Amnesty's list for death sentences handed down last year, with 1,860 sentenced.

In all, at least 3,347 people were sentenced to death in 51 countries, and as many as 27,500 people are estimated to be on death row, the group said.