Candles have been lit and protest banners hung, as a small and quiet vigil is being held outside Parliament.

It's organisers are urging the Government to hold an open and independent inquiry into allegations against the SAS raised in Nicky Hager and Jon Stephenson's latest book, Hit & Run.

The organisers aren't a formal group, just friends who feel strongly about the issue and who are associated with the Catholic Worker movement.

Spokesman Adrian Leason said the Defence Force needs be supported to adhere to the high standards of honour, to which it aspires.

He said the allegations are far too big to be left to an in-house process.

Leason said the vigil is about prayer and remembering the victims of the tragedy - a natural response in the face of something so sad.

"Today Cabinet is meeting, and they are going to need all the heavenly help they can get as they make difficult decisions as to what happens now."

Leason said he's an optimist and believes our politicians do want to do the right thing.

He said they've been provided with a great deal of evidence, and an enormous amount of public concern.

"I think they really are in a difficult position to do anything but call for a full and independent inquiry."