The invitation David Trimble extended to Amnesty to investigate paramilitary human rights abuses caused a little surprise. The relationship between unionism and Amnesty has seldom been comfortable.

Indeed, the British government's relationship with it has also often been chilly, most particularly during the Thatcher and also the Major periods.

Amnesty will send an investigative and monitoring mission to Northern Ireland, but not solely to inquire into paramilitary activity, as some inferred from recent publicity about the UUP leader's letter to the organisation.

But so-called punishment attacks form only a part of Amnesty's brief, which will also focus on alleged RUC ill-treatment of suspects, alleged RUC and British army collusion with loyalists, alleged intimidation of lawyers, emergency legislation, RUC reform and other issues.

"We had planned a mission quite a few months ago. This was not a response to David Trimble's invitation," said Halya Gowan, an Amnesty spokeswoman. Amnesty has complained that it wrote to Mr Trimble in July asking for a meeting during the forthcoming mission, and received no reply.

The UUP security spokesman, Ken Maginnis, has castigated Amnesty in the past. He claimed that by focusing on police and army actions it implicitly gave credibility to terrorism. He accused it of disregarding paramilitary abuses.

But last week, Mr Trimble said Amnesty could help bring pressure on the IRA and loyalist paramilitaries to stop "punishment" shootings and beatings.

There is a cynical, perhaps unfair, interpretation of Mr Trimble's comments: so-called punishment attacks have been hitting the headlines recently, further undermining unionists' faith in the Belfast Agreement. At least Amnesty's involvement should help illustrate that Mr Trimble is doing something practical to stop the abuses.

Mr Maginnis, despite his leader's decision to call for Amnesty's assistance, remains suspicious. "I think their temptation is to find the reality and then to excuse it in terms of unreality. That's my fear, and that's my prediction," he said. He explained that he suspected Amnesty would acknowledge paramilitaries were controlling certain communities but that it would excuse their actions in the context of the prevailing political climate.

The main criticism of Amnesty is that while it will urge the IRA, UVF and UDA to observe humanitarian law, generally as in the Geneva Convention, in relation to civilians, it will make no similar pronouncements relating to paramilitary murders of RUC officers and British soldiers.

Five years ago, following the publication of Amnesty's report Political Killings in Northern Ireland, the then Northern Secretary, Sir Patrick Mayhew, wrote to it stating that in 1993 paramilitaries had killed 85 people while the British army and the RUC killed no one.

"I think that might have found a mention in a report that expresses strong suspicions of a policy of unlawful killings by the security forces," said Sir Patrick.

"Why do you call on the paramilitaries to desist only from killing civilians? Are human rights denied by you, as well as by the terrorists, to police officers? . . . Will you now additionally call on the paramilitaries to stop killing police officers and the military who support them. If not, why not?"

Ms Gowan, recalling that letter this week, said Sir Patrick was being particularly selective: he ignored the 30 pages of a 90-page report that addressed paramilitary shootings, beatings and killings. But she confirmed that Amnesty would condemn paramilitary killings of civilians but would make no such comment about paramilitary killings of British soldiers or RUC officers.

Sir Patrick illustrated the reason for hostility to Amnesty in certain quarters. Claudio Cordone of Amnesty's policy-making department tried to explain its position. "What we are trying to say, without making a comment one way or the other about the legitimacy of the IRA, UVF or UDA, is that if para militaries claim a certain status then equally they have obligations in humanitarian law," he said.

He could understand why Amnesty's refusal to condemn certain killings could cause offence but Amnesty was not pacifist. He stressed that Amnesty was not stating that a legitimate "war" was or had been waged in Northern Ireland. It was just silent on the matter.

Throughout the Troubles, Amnesty has rankled the British government and unionist establishment. Its allegations of RUC ill-treatment of suspects, its complaints about the Birmingham Six, the Guildford Four, the SAS Gibraltar killings, claims of evidence of collusion between the security forces and loyalist paramilitaries, and allegations that the British army and RUC were not doing enough to protect Catholics, won the endorsement of nationalists but often infuriated the British authorities and unionists.

As a watchdog against human rights abuses by the authorities it has been thorough and effective. But over the past 10 years or so there have been growing calls for Amnesty to turn its sights on paramilitaries.

In 1991, Amnesty widened its mandate to include such abuses but, as Ms Gowan said, most of its work deals with state offences. Similarly, its mission will deal mainly with alleged abuses by the authorities, although the activities of the IRA, UVF and UDA will be queried.

Families Against Intimidation and Terror welcomed Amnesty's commitment to include "punishment" beatings in its brief. FAIT spokesman Mr Vincent McKenna said that because Amnesty was such a reputable organisation, its involvement would have an influence on paramilitaries, perhaps more so on republican than on loyalist bodies.

"There's been no IRA `punishment' attacks in the past nine days, which roughly coincides with the announcement that Amnesty was taking an interest," he said.

But another high-profile pressure group, Families of the Disappeared, is far from complimentary. In 1995 the organisation, which campaigns to locate the graves containing loved ones killed mainly by the IRA, met Amnesty seeking support. "The Provos were very worried that Amnesty were meeting us, but they had no need to be. I was very disappointed in them. They made it clear that they didn't generally touch that sort of thing," said spokesman Seamus McKendry.

He argued that Amnesty had a moral authority that it should and could have exercised to better effect to pressurise the IRA into identifying where the bodies were left.

Ms Gowan, who met Mr McKendry, said Amnesty had addressed the issue seriously. "But we don't deal with the IRA, we don't write to the IRA." She agreed Amnesty had direct dealings with politicians, the RUC and pressure groups, but said the IRA, an outlawed organisation, did not fall within its ambit.

Ms Gowan did not accept there was a perception that Amnesty was soft on paramilitary abuses. "We do condemn such actions. It's there to see in our special and annual reports. We take the issue seriously, and we address it seriously," she stated.