Moscow ? Police on Saturday detained several foreign rights activists trying to attend a conference commemorating Anna Politkovskaya, the Russian investigative reporter and Kremlin critic who was murdered a year ago, activists said.

The detentions occurred on the eve of the anniversary of Politkovskaya’s execution-style slaying in her Moscow apartment building entryway. Other rights activists planned commemoration ceremonies today in Moscow.

Politkovskaya won international acclaim for her reporting of atrocities against civilians in war-scarred Chechnya, and her killing cast a harsh light on the safety of journalists and government critics under President Vladimir Putin.

The five detained activists – including citizens of Spain, Britain and Germany – were among dozens who traveled to the city of Nizhny Novgorod for the conference, said Svetlana Gannushkina, the head of the nongovernmental Civic Assistance Committee.

The five were held for 4 1/2 hours at an immigration office and ordered to pay a $120 fine for violating their visas, according to the U.S.-based group Human Rights First. The group said one of its members, Neil Hicks, a British citizen, was among those detained.

Police in Nizhny Novgorod refused to comment Saturday about the detentions, and local officials could not be reached.

The Interfax news agency quoted a police official as saying, however, that the activists had been detained for breaking local registration requirements.

Conference organizers said the detentions were part of an official campaign to thwart the gathering, where participants planned to discuss the investigation into Politkovskaya’s murder as well as the state of journalism in Russia.

Organizers said authorities pressured the venue owners into reneging on a lease and encouraged hotel administrators to block reservations from some attendees.

Prosecutors also interrogated one of the conference’s organizers, Stanislav Dmitriyevsky, whose rights group, the Russian-Chechen Friendship Society, has been critical of government policies in Chechnya and was ordered closed by the Supreme Court for allegedly promoting extremism.

Prosecutors recently opened a new investigation into Dmitriyevsky and another group he was involved with for allegedly using pirated software.

He accused authorities of being terrified of renewed criticism of government policies and their failure to solve Politkovskaya’s killing.

“It’s a mad house, simply,” Dmitriyevsky told Ekho Moskvy radio. “On the one hand, this is all hysteria; on the other hand, it’s like they’re spitting on her grave, demonstratively.”