UN officials said UN remained convinced that accountability is an essential foundation for durable peace and reconciliation in Sri Lanka.
Sri Lanka has dubbed the panel "gross interference in Sri Lanka 's internal affairs and action unwarranted and uncalled for."
Sri Lanka's position is also based on the argument that it had already appointed its own commission and the responsibility of investigation lies with Sri Lanka.
The eight- member "Lessons Learnt and Reconciliation Commission " appointed by Sri Lankan President Mahinda Rajapaksa in May has started their work.
Rajapaksa appointed the commission comprising of academics and professionals to report on the issues and circumstances that led to the escalation of the ethnic separatist armed conflict since 2002.
The UN said UN offices should not be blocked and their work should continue unobstructed.
UN spokesman Farhan Haq said Wednesday at UN Headquarters in New York that staff members of the UN Country Team in Sri Lanka would return to their Colombo office starting from Thursday.
"We will continue to closely monitor the developments on the ground," Haq said. "We trust the Sri Lankan government will honor the commitments made in ensuring the safety and security of our staff so that they can continue the vital work being carried out by the UN every day to help the people of Sri Lanka."
A spokesman from the NFF said Weerawansa has determined to continue his hunger strike until Ban decided to disband the advisory panel, but the UN said the pressure through the demonstration would not cause the disbanding of the panel.
Diplomats said it is unlikely that the panel would be disbanded, but the NFF demonstration might force the UN to go slow on the panel's work.
Analysts also said the Sri Lankan government has a key role to play in the current deadlock.
