In the statement, US State Department acting spokesman Robert A. Wood said the United States was appalled by ongoing physical attacks and threats against the media in Sri Lanka, where government troops and locked in combat with Tamil separatist rebels.
It comes a day after the editor of a weekly paper, Upali Tennakoon, was stabbed and wounded outside the capital Colombo while he and his wife drove to work.
Earlier this month another newspaper editor was shot dead near Colombo.
"These serious reports are disturbing indicators of the deteriorating atmosphere for media independence in Sri Lanka," the US statement said.
"We call on the government of Sri Lanka to protect all of its citizens by enforcing law and order, preventing intimidation of the media, and by conducting swift, full, and credible investigations into attacks on journalists and other civilians.
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According to official figures, nine journalists have been killed in the past three years, while 27 have been attacke