Photo of Kem Sokha via VOA 
Via Jinja  who points to this AP wire story  about the arrest  of the Kem Sokha, Cambodian Center for Human Rights . It confirms that Yeng Virak, head of the Community Legal Education Center , was also arrested.
The article provides more details about the banners displayed at Human Rights Day that prompted the arrest. (Cambodia Blog  has a post with some photos from the December event here  and here  – but not the banner described below.) The Cambodian government also denied cracking down on freedom of expression:
Khieu Kanharith, the government spokesman and information minister, said the government has sued the two men over a critical banner they displayed during a gathering on International Human Rights Day on Dec.10. He said the banner labeled Hun Sen as a "communist" and a "traitor who has sold away (Cambodian) land to Vietnam."
"We have already stated in the past that this (accusation) is very serious," he said, denying the government is cracking down on freedom of expression.
U.S. Ambassador Joseph Mussomeli suggested in his comments that the latest action shows the Cambodian government is more authoritarian than democratic. In an article in the Cambodia Daily , Mussomeli said "We are concerned that this may be part of a broader plan to
quash the opposition. The prospects for a credible and fair election in 2008 are being impaired…. They've scared the hell out of the opposition and it becomes more difficult to take these trappings of democracy as the real thing."
Virak's lawyer said the arrest is unfair as the words on the banner in question were scribbled by someone else and that when the organizers saw it, the banner was promptly removed. Still some argue, a government tolerant of free speech would not be throwing the organizers of the event or the organization holding the banner in jail.
Those blogging fromoutside the country  expressed dismay  about recent events. According to an article  in the Cambodia Daily, for some Cambodians citizens quoted in the article, the arrest is a warning to stop speaking out. One unidentified source quoted in the article is calling for outside help:
"The UN and powerful countries around the world should intervene on this matter in order to help those activists," he said. "Then Cambodian people can take the second step in protesting to release Kem Sokha and others."
Expat Cambodians  living in the US are organizing and urging US citizens to contact
their government officials to express outrage about the situation. Here is an opinion piece from the Cambodia Information Center blog entitled Freedom Of Expression Being Haunted By Ghost Of The Past which is also encouraging people to speak out.