The BBC has been banned for a third time from covering an official panel's investigation into the final phase of the Sri Lankan civil war.
The panel visited Tamil prisoners at a top-security jail in Boosa in the south of the country.
But the BBC correspondent and a number of Sri Lankan journalists were turned away at the prison gates.
The 26-year conflict ended in May last year with victory for government forces over the Tamil Tiger separatists.
The BBC's Charles Haviland says Boosa jail holds about 700 Tamil Tiger suspects, some of whom have been detained for years without trial.
On Wednesday, a defence ministry official told our correspondent and other journalists they could visit the jail to witness meetings between prisoners and the war commission.
But upon arrival on Thursday, all reporters were denied entry and the same defence ministry official, speaking by telephone, denied having given permission, says our correspondent.
Officials from the prison and the war panel apologised, but said they could not get the media admitted.
The panel has visited several detention facilities, but this would have been the first chance for the media to go inside with them.
It is the third time that the BBC has been barred from covering the panel's proceedings since it began work in August - previous bans have been followed by official apologies.
The political detainees at Boosa prison have been held under anti-terrorism laws and are described by the government as "hardcore".
Our correspondent says rumours have persisted that Tamil prisoners have been tortured in the jail, which is flatly denied by the government.
Human rights groups including Amnesty International have declined to testify at the commission because they say it is not independent.