Sri Lanka's military stopped scores of ethnic Tamil protesters from entering the capital on Wednesday before a Commonwealth summit as a British TV crew also faced problems travelling around the island.
Roman Catholic priest Emmanuel Sebamali, who organised the visit by minority Tamils to the capital, said their buses were stopped initially by police and later by troops who forced them to return.
"We have been forced to turn back," the priest told AFP by telephone. "They've refused to give us a reason. They just won't allow us to travel to Colombo."
The Commonwealth Heads of Government Meeting (CHOGM), set to begin on Friday, was hit by a new pullout Tuesday as the prime minister of Mauritius joined those of India and Canada in boycotting the event.
Sri Lanka had hoped the three-day summit would showcase its post-war revival but it is turning into a PR disaster as some of the 53 Commonwealth members and rights groups focus attention on the island's human rights record.
Sebamali said that about 200 Tamils were en route to a meeting to draw attention to the plight of thousands who lost loved ones in a decades-long separatist war which ended in 2009.
The final government offensive has been dogged by war crimes allegations, with Sri Lankan troops accused of murdering surrendering rebels and shelling hospitals. Colombo denies any wrong doing.
There was no comment from police or the military on the Tamil protest, but Media Minister Keheliya Rambukwella said the authorities prevented them from travelling to Colombo fearing a "breach of the peace".
"There were intelligence reports that this is a politically motivated protest and these (Tamil) people came to Colombo during the summit, it would have led to a breach of the peace," Rambukwella told reporters.
A group of Tamils was similarly stopped in May by authorities who cited safety reasons, saying they could be attacked by opponents en route to Colombo.
Britain's Channel 4 TV crew, who faced a pro-government protest on arrival Monday, had more trouble travelling to the former war zone in the northeast Wednesday.
Hundreds of pro-government activists carried placards accusing the channel of supporting the defeated rebels and blocked their train from leaving the north-central town of Anuradhapura.
Callum Macrae, director of Channel 4's award-winning documentary: "No Fire Zone: Sri Lanka Killing Fields", said police told them they must return to Colombo.
British Foreign Secretary William Hague raised the issue with his Sri Lankan counterpart Gamini Lakshman Peiris during ministerial level talks ahead of the Commonwealth summit.
"Concerned to hear the incident with Channel 4 news," Hague said on Twitter. "Have raised with Foreign Minister Peiris."
Minister Rambukwella said they could not intervene and stop the anti-Channel 4 protest as it was "peaceful".
Sri Lanka grounded private domestic flights during CHOGM as a security move which also impeded foreign journalists who planned to fly to Jaffna, the Tamils' cultural capital.
It takes eight hours to travel the 400-kilometres (250 miles) from Colombo to Jaffna by land while flying takes an hour.
On Tuesday hundreds of Tamils began a separate protest in Jaffna, pressing authorities to return military-occupied land.
The organiser, Sugirthan Somasundaram, said slaughtered cow heads were thrown into his home and that of another organiser Sunday, along with a note warning them to abandon their demonstration.
They vowed to keep up the protest until British Prime Minister David Cameron visits Jaffna during his trip to attend the Commonwealth summit.
A UN panel in 2011 found that as many as 40,000 civilians may have been killed in the final months of the civil war in 2009, mostly because of Sri Lankan military action. But Colombo denies its troops killed any civilians.