Media playback is unsupported on your device Media caption Judith Thompson called for a "clear definition" of national security to resolve the issue.

Northern Ireland's victims commissioner has said the government cannot use national security as a rock under which to hide from Troubles-related issues.

Families of people killed by security forces claim it is being used to block access to information on the killings.

Victims commissioner Judith Thompson called for a "clear definition" of national security to resolve the issue.

She also said the current process on dealing with the Troubles' legacy could be the "last chance" to get agreement.

"A workable deal is still very much on the cards and while I accept it will have to wait until after the Assembly elections, I am very clear that if we don't get it now, I don't know when we will get any closer to a point where all the pieces are in place," the commission warned.

'Convenient rock'

The deadlock over access to official documents is delaying the full implementation of the Historical Investigation Unit (HIU), the new independent body set up to investigate Troubles-era killings.

The government has argued that the release of some state documents could compromise national security and put lives at risk.

Image caption Earlier this month Theresa Villiers said the government has concerns about the release of information on Troubles cases. either because it could put lives at risk or compromise the security services' capabilities

But speaking ahead of a conference on the victims' issues, Ms Thompson said: "National Security cannot be a convenient rock under which the government can hide uncomfortable issues.

"Neither can there be an excuse for anyone refusing to come forward to cooperate with the proposed new Historical Investigation Unit or Independent Commission for Information Retrieval."

"Doing nothing is not an option," she added.

Ms Thompson said the lack of progress in last year's Fresh Start Agreement was "gut-wrenchingly disappointing" for victims.

The lack of an agreed way forward on how to deal with the past was the key issue on which the 2015 talks failed to produce a resolution.

'Really close'

The victims' commissioner said the people she represents still felt let down by politicians' failure to reach agreement on the ongoing difficulties they face.

"It left victims and survivors wondering whether they had just been led up the garden path," Ms Thompson said.

"But my view - and having talked to people who were involved in that process is - we weren't led up the garden path, there was genuinely progress made.

"We came really close, but we've got to do it. Close isn't good enough," she added.

Earlier this month, Northern Ireland Secretary of State Theresa Villiers defended the government's approach to the release of state documents related to the Troubles.

She she said the government has legitimate concerns about what the Historical Investigation Unit might then make public - either because it could put lives at risk or compromise the security services' capabilities.

Ms Villiers warned that dissident republicans and Islamist militants should not be shown how UK security services work.