The United States is sending an FBI agent to Azerbaijan to help find those responsible for the killing of magazine editor Elmar Husseinov, whose work was critical of the Azeri government.
The U.S. Embassy said the agent is arriving in Baku Friday at the request of Azerbaijan's government.
President Ilham Aliyev ordered a swift investigation, calling the attack a serious provocation against the state and authority.
Earlier, the country's top opposition leader called for demonstrations in response to Wednesday's killing.
Mr. Husseinov was the editor of the weekly Monitor. He had previously been jailed and fined for his work.
The Committee to Protect Journalists said the killing appeared to have been well-planned and orchestrated -- while the Paris-based Reporters Without Borders called it part of a campaign of violence against journalists in Azerbaijan.
Some information for this report provided by AP.