The United States is sending a special FBI agent to Azerbaijan to help find those responsible of the killing of magazine editor Elmar Huseynov.
Huseynov was fiercely critical of the authorities
The agent is due to arrive in the capital Baku on Friday to meet officials working on the investigation.
Huseynov's funeral is scheduled to take place on Friday amid growing unrest.
Opposition leaders have already announced they will try to transform the funeral into an anti-government demonstration.
"I propose to all who are concerned with the fate of Elmar Huseynov to get together, bid our farewells and express our hatred for the current regime," said Ali Kerimli, who leads the National Front opposition party.
But after holding a security council meeting, Azeri President Ilham Aliyev warned he would not allow any political force to "use this killing to advance their own ambitions".
He also said he was willing to let foreign experts help the investigation into the murder.
Earlier on Thursday, the US embassy said "everything possible" should be done to bring his killer or killers to justice.
"Elmar Huseynov's death is a great loss to the ongoing development of democracy and press freedom in Azerbaijan," it said in a statement.
The Council of Europe's human rights monitoring body on Thursday condemned the killing as "an attack on freedom of expression in Azerbaijan".
The country's human rights groups have linked the murder to his journalistic activity editing the magazine Monitor, which had been closed down several times for running articles critical of politicians and businessmen.
Huseynov, who was strongly critical of the Azeri government, was shot dead in front of his home on Wednesday.
Mr Aliyev succeeded his father as president in 2003.
The elections were criticised by international observers, and were followed by violent protests.
Several opposition leaders were jailed in connection with the riots.