A South Sudanese reporter often critical of the government has been shot dead at his home in the capital Juba, colleagues say, adding that he been recently threatened to stop writing.
Diing Chan Awuol, who wrote for news websites including Sudan Tribune and Gurtong under the pen-name Isaiah Abraham, was shot dead by unidentified men in his home in the early hours of Wednesday morning, police said.
"Police are investigating and they will be discovering what happened... they suspect an assassination as nothing has been stolen," said police spokesman James Monday Enoka.
One of his last articles urged Juba's government to improve relations with former civil war foes in Khartoum and stop any support for Sudanese rebel groups.
"Journalists said Chan had been threatened several times in the past and had received anonymous phone calls warning him to stop writing," the US-based Committee to Protect Journalists said, calling for a "thorough investigation".
"His real name was recently discovered and as a friend, he told me that security agents are after him," said a friend of Awuol, who asked not to be named.
"I advised him to abandon using 'Isaiah Abraham' and create a different pseudonym, but it was too late."
South Sudanese journalist Ayuen Panchuol said the killing was a way of saying "look, this is what will happen to you if don't shut up".
South Sudan, the world's newest country after it split from Sudan in July 2011 following decades of war, is struggling to rebuild basic institutions.
Awuol, who was married and with five children, fought with the South Sudanese rebels who battled Khartoum from 1983-2005, now the official army of the fledgling country.
Most recently he worked at the national justice commission.