Malcolm Turnbull says there's too much tolerance of extremist material on social media and wants tech giants Facebook, Twitter and Apple to help tackle terrorism.

His comments echo those of British Prime Minister Theresa May who declared "enough is enough" following the deadly terrorist attack in London at the weekend - the third in the UK in as many months.

Mr Turnbull says Ms May has put her finger on an important point.

"There is too much tolerance of extremist material on social media and that, ultimately, requires co-operation from the big social media platforms - in particular, Facebook and Twitter," he told reporters in Sydney on Monday.

"It is one of the priorities that we have ... to get a more responsible approach taken to this type of material."

He said authorities also needed help from companies like Whatsapp and Apple in providing access to encrypted messaging used by billions of people.

It was important for security services, he said, noting the difficulty the FBI had getting into the iPhone of a terrorist involved in the 2015 San Bernardino attack.

While Syria and Iraq might be a long way from western Sydney, electronically they were closer than ever, he said.

"There are no borders ... that is why we need much greater co-operation," Mr Turnbull said.

Foreign Minister Julie Bishop said posts on social media that encourage radicalisation need to be dealt with in a similar way to child pornography.

"Everyone knows when child porn goes up on the internet it can be taken down," She told ABC's 7.30 program on Monday night.

"When the kind of posts that incite hatred and violence and radicalisation and teaching people how to carry out these savage, positively medieval attacks, then there should be an ability to take that kind of post down immediately.

"This kind of material is dangerous. It's a risk to our communities."

At least four Australians were affected by the latest attack in London, with two injured and grave concerns about two others.

The prime minister, ramping up his rhetoric, branded it the work of "cowardly, crazed criminals".

Their evil message was a "blasphemous corruption" of Islam and millions of Muslims around the world.

"(They're) trying to poison the religion from the inside and threaten our way of life," he said.

"We defy them and we reject the poisonous ideology that they peddle. We will never give in to terrorism. We will never change the way we live."

Earlier, former prime minister Tony Abbott renewed his call for the military to be used in complex terrorist situations.

He said the strongest possible response was needed, warning that all too often in officialdom's ranks Islamophobia was seen as big a problem as Islamist terrorism.

"Islamophobia hasn't killed anyone, Islamist terrorism has now killed tens of thousands of people," Mr Abbott said.

Mr Turnbull said the role of the defence force in terrorist incidents was being reviewed following the Lindt cafe siege.

As it stands, the SAS can only intervene if requested by the state government.