The Free Media Movement (FMM) said a workshop organised by them for journalists northern Jaffna peninsula, a former conflict zone, was abandoned after threats by pro-government groups.
"A group of people came and demonstrated opposite our office today forcing us to cancel the workshop," said FMM convener Sunil Jayasekera.
"We were concerned about the safety of the journalists and that is why the training was called off."
"They carried placards saying that we are supporting (separatist) Tamil Tigers (guerrillas)," Jayasekera told reporters.
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Sri Lanka's largely Sinhalese army was locked in a three-decade conflict with the Tamil rebels which ended in 2009. The ethnic conflict had left over 100,000 dead.
In a separate incident, United Socialist Party leader Sirithunga Jayasuriya said a motorcycle parade organised by his party to promote inter-community peace was also disrupted.
"The police told us not to proceed halfway through the parade. They said the order was for our own safety," said Jayasuriya.
He said they attempted to travel to the southwestern regions of Aluthgama and Dharga town, the scenes of communal violence in mid June in which four people were killed, with a message of peace.
The Muslim minority was allegedly targeted in the communal violence blamed on the Buddhist nationalist group, BBS.