The International Federation of Journalists has described the murder in Moscow of Anna Politkovskaya as a "shocking outrage that will stun journalists across the world."
The IFJ says the killing reflects a state of lawlessness that is threatening to overwhelm Russian journalism. It has called on the government of President Vladimir Putin to act immediately to bring the killers to justice.
Politkovskaya was shot dead on Saturday. According to news reports, her body was found in the lift in the building where she lived.
"The Russian authorities must carry out an urgent and intensive investigation. We need to know who killed our colleague and who ordered the attack in the first place," said Aidan White, IFJ general secretary.
Politkovskaya, who worked for the newspaper Novaya Gazeta, established her reputation on the back of controversial reports about human rights abuses by Russian troops in Chechnya.
Her reputation and trenchant reporting made here a thorn in the side of the Russian government and when she fell seriously ill with food poisoning in 2004 while on her way to report on the Beslan school siege, many observers believed it was an attempt on her life.
"She was the bravest of the new breed of brave reporters who emerged in the dying days of the Soviet Union," said White. "She faced down threats from all sides and was an inspiration to journalists both at home and abroad. Her death is a shocking outrage that will stun the world of journalism."
The IFJ has also condemned the killing of two German journalists by insurgents, thought to be Taliban fighters, in northern Afghanistan on Saturday.
Karen Fischer, 30, and Christian Struwe, 38, were working for the German network Deutsche Welle on a documentary project when they were killed. They had been travelling through the northern province of Baghlan, about 100 miles Northwest of Kabul, and had stopped outside a village, where they set up a tent to spend the night. They were killed by attackers using AK-47 assault weapons.
"These deaths once again demonstrate how journalists are at risk in conflict zones," said White.
"This shocking and tragic event brings home to all of us the need to strengthen protection for journalists in the field."
Deutsche Welle said they the journalists were conducting research for a documentary and were en route to the province of Bamian, where two large Buddha statues were destroyed by the Taliban in early 2001.