Australia’s human rights commissioner has warned that governments must be wary of trading away liberties for security and any such measures should be temporary.

Tim Wilson, who was appointed by the Abbott government to the Human Rights Commission to champion freedom, said changes to the nation’s counter-terrorism laws must be supported by evidence “that they are necessary to protect people and not just to be an ambit claim by government or police or security agencies for more powers”.

Tony Abbott told parliament on Monday that Australians should prepare for a shift in “the delicate balance between freedom and security” for “some time to come” as part of the fight against domestic terrorism threats.

Separately, the prime minister’s office said Australian agencies believed an inflammatory new statement attributed to Islamic State (Isis) was genuine.

The Isis statement called on followers to resist “a new campaign by the crusaders” and to kill disbelievers, whether civilian or military, from Australia and other countries that had “entered into a coalition against the Islamic State”.

In a written response provided to some media outlets, Abbott’s office dismissed the claim that Australia was targeted for its willingness to participate in military action in Iraq, saying “these people do not attack us for what we do but for who we are and how we live”.

Making the case for the biggest overhaul of the Australia’s counter-terrorism laws in a decade, Abbott said: “There may be more restrictions on some so that there can be more protections for others. After all, the most basic freedom of all is the freedom to walk the streets unharmed and to sleep safe in our beds at night.”

Parliament will soon debate the government’s first national security legislation bill to expand the powers of intelligence agencies and criminalise disclosure by any person of covert “special intelligence agencies”.

A second bill, targeting Australians suspected of fighting in Syria and northern Iraq, will be presented to parliament on Wednesday and will include a new offence of travelling to a government-declared region without a legitimate purpose.

The attorney general, George Brandis, confirmed a prosecutor would have to prove that a person had travelled to, or remained in, designated “no-go zones”, and it would be up to the defence to mount a successful argument that the person was there for a legitimate purpose.

Wilson said he was “calm” about the mooted no-go zone provision so long as it was done in a way that did not victimise one section of the community.

But he issued a broader call for caution as the parliament prepared to consider a raft of changes.

“Obviously security of the person is absolutely essential in making sure that we can preserve our rights and freedoms but laws should not become too restrictive so we don’t end up trading off security for freedom,” Wilson told Guardian Australia.

He said security powers should “be put under public and parliamentary scrutiny to make sure we get the balance right”. The resulting legislation “should have sunset clauses and review clauses to make sure that if there is any surrender of freedoms for security that it is only ever temporary”.

On Monday Brandis announced several concessions in response to concerns raised by the Islamic community, the Labor opposition and the Liberal Democratic senator David Leyonhjelm.

These include amending legal immunities for Australian Security Intelligence Organisation (Asio) officers conducting covert “special intelligence operations” to specifically exclude torture. Other contentious measures, such as the new no-go zone provision, would expire in 10 years unless a future parliament granted an extension.

A prominent member of the Islamic community, Keysar Trad, said the changes were welcome but did not allay his concerns about the extent of changes.

The Islamic Friendship Association of Australia spokesman said the nation must ask whether it was prepared to give away its liberties “because we’re in a state of fear”.

Trad raised practical concerns about how people might prove that they had travelled for a legitimate purpose and the need for people to be given a fair hearing.

“You might be able to say, I was looking after my grandmother for most of this time. The question that will come back to you is: were you looking after her 24 hours a day? You’ve accounted for eight or three hours of every day; how do you account for the rest of your time? That is onerous and whether we want to admit it or not that is already a presumption of guilt.”

Trad argued that the terrorism raids in Sydney and Brisbane last week were evidence the existing powers of police and security agencies were “more than adequate”.

“We do care about our safety as a nation,” he said. “But what does safety and security mean if you have no freedom, if you lose your basic freedoms? I understand that they have a duty and a role to protect the nation. I genuinely respect that role and we want to be partners in protecting the nation but we don’t want to be rubber-stamping an exercise that takes away freedoms.”

The president of the Queensland Council for Civil Liberties, Michael Cope, said once governments changed fundamental legal principles in an area such as terrorism, they cleared the way for similar changes in other areas.

Cope said the federal government must demonstrate the extra powers were necessary and would make a difference.

“The problem is that if you want to have liberty it results in a certain level of insecurity,” he said. “At the end of the day everyone in the country has to make a judgment call about where that line is.

“Once you move the goalposts in area A, they rapidly move to areas B, C and D. It’s all very well for the prime minister to say these are temporary measures but they were meant to be temporary measures a decade ago.”

The Greens senator Scott Ludlam told the ABC’s Q&A program he had a “fundamental problem with the idea that to protect our freedoms we need to abolish them” and it was unsurprising that intelligence agencies wanted more power.

The justice minister, Michael Keenan, a fellow panellist on the program, said the government was acting on the advice of police and security agencies, which he described as “diligent public servants” seeking to ensure community safety.

Keenan rejected any suggestion of a conspiracy surrounding the timing of last week’s raids, saying the police chose when to act and briefed him only a short time beforehand.