The arrests of Cambodia's two top human rights activists has raised fears the nation is headed toward dictatorship again.

Kem Sokha and Yeng Virak are awaiting trial on criminal defamation charges related to a banner criticizing Hun Sen, the country's prime minister and strongman. They join a growing number of government opponents behind bars.

"Cambodia right now is at a crossroads. It must decide whether it's going to be a real democracy or whether it's going to move inexorably toward a one-party state," said U.S. Ambassador Joseph Mussomeli after watching Kem Sokha's arrest Saturday at the Cambodian Center for Human Rights office.

After the murderous Khmer Rouge years, and the 1980s under a communist regime installed by neighboring Vietnam, a 1993 election offered the hope for democracy taking root.

However, in 2003 the government banned all public demonstrations on the pretext of keeping order following street protests against Thailand, and now it is restoring to suing opponents for critical comments about the sensitive issue of border demarcation with Vietnam.

The lawsuits have landed a radio journalist and a union activist in jail, and a nephew of retired King Norodom Sihanouk has had to flee Cambodia.

But perhaps most serious have been government blows against the already emasculated political opposition to Hun Sen, a onetime Khmer Rouge commander.

Last month, a court sentenced self-exiled opposition leader Sam Rainsy to 18 months in prison for accusing Hun Sen of being behind a 1997 grenade attack on peaceful demonstrators in Phnom Penh and alleging that National Assembly President Prince Norodom Ranariddh took bribes from Hun Sen in exchange for joining the government in 2004.

"When you have intimidated the opposition so much and you have arrested most of their leaders, and others have had to flee into exile, there is not much left to the opposition, and that means there's not much left to a real democracy," Ambassador Mussomeli said, echoing similar recent statements by the United Nations and human rights organizations.

Hun Sen, whose Cambodian People's Party won the 2003 general election, says Sam Rainsy preaches the rule of law yet refuses to abide by legal decisions.

"He has accused me of being a killer. Now if he has the guts, he should come back to serve his prison sentence as convicted," Hun Sen said recently.

Hang Puthea, director of the Cambodian election watchdog Nicfec, said Sam Rainsy may have erred in failing to provide solid proof of his claims against the regime.

"But his whole case has been overwhelmingly dictated by politics rather than justice," he said, referring to a judicial system that is known for being corrupt and susceptible to political influence.

Som Chandyna, Sam Rainsy's lawyer, said his client also risks being barred from running in the 2008 election. He cited the case of opposition member Cheam Channy, who is serving a seven-year jail term.

Cheam Channy, who headed an opposition party committee to gather information about defense and security matters, was accused of trying to recruit an armed group to oppose the government. The international community has strongly criticized the charges against him.

The chilling effect of the lawsuits is evident in the guarded responses of Kek Galabru, president of the Cambodian human rights group Licadho, during an interview.

"We are still far away from a democracy," he said. "I have to be careful because anything now can be picked up and used as defamation."