"The detention of these journalists and media workers is troubling," said CPJ executive director Joel Simon said in a statement.
"The Sri Lankan government must clarify why they are being held and either charge them or release them immediately.
"The fact that four of them are Tamil journalists and media workers is an indicator of how vulnerable this group is to harassment by the Sri Lankan authorities."
Six individuals, connected to the multimedia news Web site OutreachSL.com, were detained separately between Thursday and Saturday last week, The Free Media Movement (FMM), a Colombo based media rights body said.
OutreachSL editor J S Tissanayagam also writes a column for the Sri Lankan English weekly, The Sunday Times. S Ranga, a photographer; K Wijesinghe, a video cameraman; vis