The United Nations has threatened overnight to suspend aid operations in Sri Lanka after truce monitors accused the security forces of executing aid workers.
Nordic truce monitors formally accused the security forces of being behind the execution-style murders of 17 local staff of aid agency Action Contre La Faim earlier this month in the northeast.
The government denies the allegation.
"We have no independent information ourselves in the UN, but I say we cannot continue in this area unless people will be held accountable for the execution of 17 of our colleagues," UN Emergency Relief Coordinator, Jan Egeland, told reporters in New York.
The victims, mostly Tamils, were found shot dead in their compound in the northeastern town of Mutur, around 135 miles northeast of the capital Colombo. It was the worst mass murder of aid staff since a 2003 bomb attack on the United Nations compound in Baghdad.
The Nordic Sri Lanka Monitoring Mission (SLMM) says Sri Lankan authorities have obstructed their efforts to investigate, and that it is convinced no armed groups other than the security services could have been responsible.
The last of the SLMM's European Union members are due to cease work on Thursday, the deadline of a rebel ultimatum for them to leave the island after the 25-nation bloc banned them as a terrorist organisation.