Jack Straw today said he would take the unprecedented step of vetoing the release of cabinet minutes relating to the decision to invade Iraq.

The justice secretary made his announcement in response to a decision from the information tribunal, which last month ordered the publication of the minutes of two cabinet meetings, held on 13 and 17 March 2003.

It is the first time the government has used its power to veto the release of documents under the Freedom of Information (FoI) Act .

In a statement to MPs, Straw said he had not taken the decision "lightly".

He added that the public interest in disclosure of the minutes could not "supplant the public interest in maintaining the integrity of our system of government".

"It is a necessary decision to protect the public interest in effective cabinet government," he said.

Straw's decision was supported by the Tories, although the shadow justice secretary, Dominic Grieve, said the government should have made it clear earlier that it was not going to release the minutes.

Under the FoI legislation, the government does not generally have to release information relating to the formulation of policy.

However, the tribunal ruled that this was an exceptional case because of the public interest in knowing what was said as ministers discussed the decision to approval the invasion.

Straw told MPs he disagreed with the tribunal's findings.

He said confidentiality was most important when the cabinet was discussing the most sensitive issues.

"Cabinet is the pinnacle of the decision-making machinery of government," Straw said.

"It is the forum in which debates on the issues of greatest significance and complexity are conducted.

"This matter – whether the nation took military action – was indisputably of the utmost seriousness."

He said he disagreed with the argument that the "momentous" nature of the decision meant the minutes should be made public.

"The convention of cabinet confidentiality and the public interest in its maintenance are especially crucial when the issues at hand are of the greatest importance and sensitivity," he said.

"Responsibility for cabinet decisions is with the government as a whole, not with individual ministers ... that remains the first principle of the ministerial code.

"If permitted to demonstrate their degree of attachment – or otherwise – to any given policy, ministers could absolve themselves from responsibility for decisions which they have nevertheless agreed to stand by.

"The conventions of cabinet confidentiality and collective responsibility do not exist as a convenience to ministers.

"They are crucial to the accountability of the executive to parliament and the people.

"The concomitant of collective responsibility is that debate is conducted confidentially. "In short, the damage that disclosure of minutes in this instance would do far outweighs any corresponding public interest in their disclosure."

Straw said the decision to go to war had already been extensively investigated by a series of official inquiries.

"The decision to take military action has been examined with a fine-toothed comb," he said. "We have been held to account for it in this House and elsewhere."

He also said although 1,500 FoI requests relating to government information had been considered by the information commissioner, the government had not, until now, used its power, under section 53 of the FoI Act, to issue a ministeral veto.

The two cabinet meetings were particularly controversial because they occured at a time when ministers were considering the legality of going to war.

Lord Goldsmith, the attorney general at the time, initially suggested that the legality of the invasion was questionable,

He subsequently issuing legal advice saying it would be safe for Tony Blair to proceed with the attack. Campaigners wanted to see the minutes to find out whether this issue had been fully debated by ministers at the time.

Responding to Straw's statement, Grieve said the decision not to release the minutes "... classically illustrates what has been wrong with the government's approach to freedom of information and propaganda".

Referring to the fact that Straw had been foreign secretary at the time of the invasion, Grieve questioned how it would look to the public "for someone so closely involved in the key decisions now to be personally blocking the release of that information".

However, he said the Conservatives agreed with the decision.

David Howarth, the Lib Dem justice spokesman, said: "This decision has more to do with preventing embarrassment than with protecting the system of government."

Like Grieve, he called for a full inquiry into the Iraq war.

Kate Hudson, the chair of the Campaign for Nuclear Disarmament, said: "This disgraceful decision is yet another attempt to suppress public debate on the biggest political scandal in decades.

"The use of the veto cannot be justified in any way – there is no risk to candid discussions in cabinet as such minutes do not single out those making each point.

"We had hoped that, with the withdrawal of the last British troops expected in a matter of months, the government would have released these minutes in preparation for the full inquiry into the Iraq war, long promised by Gordon Brown."

In its ruling last month, the information tribunal said: "We have decided that the public interest in maintaining the confidentiality of the formal minutes of two cabinet meetings at which ministers decided to commit forces to military action in Iraq did not, at the time when the Cabinet Office refused a request for disclosure in April 2007, outweigh the public interest in disclosure.

"We have reached that decision by a majority, and not without difficulty.

"We concluded that there was a strong public interest in maintaining the confidentiality of information relating to the formulation of government policy or ministerial communications (including, in particular, the maintenance of the long-standing convention of cabinet collective responsibility).

"However, this is an exceptional case, the circumstances of which brought together a combination of factors that were so important that, in combination, they created very powerful public interest reasons why disclosure was in the public interest."