They urged authorities Monday to conduct a full and transparent probe into the attack on Rasim Aliyev and to bring the assailants to justice.

Officials connect the attack with a Facebook post on Saturday in which Aliyev criticized a popular soccer player in Azerbaijan.

Aliyev said Cavid Huseynov, a striker for Gabala FK, should be banned from European football for allegedly making a rude gesture at a Cypriot journalist. 

Threatening Messages

According to local media reports, Aliyev was beaten up on Saturday after he was lured to meet an unidentified man who claimed to be a relative of Huseynov.  He underwent surgery at a hospital due to massive internal injuries and died on Sunday.

"I came out alone," Aliyev said before he died.  "There were five or six of them, and they immediately threw themselves at me and started beating me up."

Authorities in Azerbaijan say the attack is under investigation.  Azerbaijani news agency Turan reported that one of the suspected attackers has been detained, identifying him as Elsan Ismayilov, a cousin of Huseynov.

Rights groups said the before the Huseynov posting, Aliyev had already been receiving threatening messages connected to photos he had posted online showing police brutality and social discontent.

He had been an employee and board member of Azerbaijan's leading media freedom organization, the Insitute for Reporter's Freedom and Safety (IRFS), until it was closed by authorities last year.

President Concerned

The Azerbaijan Press Agency (APA) quoted a senior official who said President Ilham Aliyev is "seriously concerned" about the killing of Rasim Aliyev.  The official, Ali Hasanov, added that the president described the incident as a "threat" to freedom of speech and said ensuring the freedom of mass media is a priority of Azerbaijan's government.