Sinn Fein, the SDLP and a victims' group last night called on Secretary of State Karen Bradley to resign after controversial comments on security force killings.
Mrs Bradley's claim that such acts were "not crimes" provoked fury from nationalist politicians, who are to raise the issue with the Prime Minister.
Responding in the House of Commons to a question about legacy issues from DUP MP Emma Little-Pengelly, the Secretary of State said: "Over 90% of the killings during the Troubles were at the hands of terrorists - every single one of those was a crime.
"The fewer than 10% that were at the hands of the military and police were not crimes.
"They were people acting under orders and under instruction and fulfilling their duty in a dignified and appropriate way."
Next week prosecutors will announce whether soldiers will face trial for the Bloody Sunday killings of 14 innocent civilians in Londonderry.
Mrs Bradley later returned to the chamber to clarify her comments.
"I was not referring to any specific cases, but expressing a general view," she said.
"Of course, where there is evidence of wrongdoing, it should always be investigated, whoever is responsible.
"These are, of course, matters for the police and prosecuting authorities, who are independent of the Government."
Sinn Fein deputy leader Michelle O'Neill last night said she had told Mrs Bradley "in the strongest possible terms" that her comments were "beyond unacceptable" and that it was "a resignation matter".
Ms O'Neill said it was an issue which went "right to the heart of British Government policy". Denouncing the remarks as "outrageous and offensive", she added: "These comments are an insult to families who have lost loved ones at the hands of the British Army, state agencies and their proxies in the loyalist death squads, which were directed by the British state."
Sinn Fein president Mary Lou McDonald said she had written to both the Prime Minister and the Taoiseach about the remarks, which she said had "caused great distress to the many victims of British state forces".
SDLP leader Colum Eastwood tweeted: "Karen Bradley is publically (sic) interfering with the rule of law. No one has the right to deliberately pressure or intervene with due process. She should resign."
Mr Eastwood said the Secretary of State was again exhibiting "her stunning ignorance about the past". Her comments were "particularly insensitive given that the Bloody Sunday families await news on whether former British soldiers will be prosecuted for murdering 14 innocent civilians in Derry", he added.
Relatives for Justice chief executive Mark Thompson slammed Mrs Bradley's comments as "odious, disgusting and deeply offensive".
He said: "Rather than the miserable spectacle of 'clarifying in case she is misunderstood', Karen Bradley should resign.
"Further, her Government is neither fit nor neutral to take forward proposals to deal with the past.
"Both Governments should move to appoint an international body that can take forward a comprehensive, independent process on legacy based on the Stormont House Agreement."
DUP MP Sir Jeffrey Donaldson said there must not be a one-sided approach to dealing with the past. "We have been involved in discussions with the Government to support our veterans against the witch hunts against them," he said. "However no one should be above the law and all innocent victims deserve justice.
"Sinn Fein need to face up to the reality that they have denied IRA involvement in murders and continue to glorify terrorism. If there is to be justice, it should not be one-sided."
Victims campaigner Willie Frazer congratulated Mrs Bradley on her remarks.
"It's about time that the British Government resolutely and unquestionably supported those many veterans who served in Northern Ireland, upholding law and order with honour and distinction," he said.
"The continual and systematic attempts to discredit and blacken the forces of law and order need to be recognised as a calculated, unashamed campaign, orchestrated and prolonged by republican apologists."
Alliance leader Naomi Long said Mrs Bradley comments represented an "unwarranted and unjustifiable act of political interference" in the justice system which "undermined due process and the rule of law".
Her remarks were also "appalling and deeply hurtful" to families still waiting justice, she added.
Green Party leader Clare Bailey said the comments "constitute a new low for the Secretary of State".