The world’s major internet companies are attending a G7 summit for the first time, in an urgent attempt to draw up tough new rules to counter the dramatic rise in the use of social media by terrorists.

These talks with multinationals at the meeting, which began today in Italy, come amid deep concern that the volume of Islamist traffic on tech platforms will increase even more, as Isis tries to compensate for its defeat in Syria and Iraq by instigating attacks in the West online.

Global corporations have been invited to the conference at Ischia in the Bay of Naples, which will also consider steps to cope with the impending return of hundreds of European jihadists who went to fight with Isis and al-Qaeda.

The issue of internet radicalisation has been taken up to the level of G7 – the governments of the US, UK, Germany, France, Italy, Canada and Japan -- after warnings by counter-terrorism officials of an ongoing Islamist offensive. Earlier this week the head of MI5, Andrew Parker, spoke of Britain facing unrelenting attacks at an unprecedented scale.

This was partly fuelled, he said, by extremists finding motivation and material online, from indoctrination to bomb-making tutorials, as well as explosives available for purchase.

laine Duke, the acting US secretary of homeland security, speaking in London on her way to the summit, said: "The fact that the companies are meeting with us at G7 is a positive sign. I think they are seeing the evidence of it [terrorist use] being real and not just hyperbole.

“There are a lot of social pressures and they do want to do business, so they have to balance between keeping their user agreements and giving law enforcement what they need.

“We would like to have the ability to get encrypted data with the right legal processes. We will continue to push as far as we can go. I think we have the cooperation of these companies and we need to work on that.”

Ms Duke, who met Home Secretary Amber Rudd on Wednesday, said that America and Britain will be pressing for more security measures to be taken by the internet service providers. Details are yet to be worked out, she said one option could be finding a suitable algorithm to detect and remove dangerous material, the way US authorities search airline records for suspects trying to enter the country.

UK law is expected to be changed so that those who repeatedly view extremist content online can face a possible sentence of 15 years behind bars.

The US, said Ms Duke, faced more of a threat from homegrown terrorists being influenced on social media than from those trained abroad.

She said that much of the extremist threat is not related to Islamic terrorism. The issue of online subversion was brought into focus in the US during white supremacist violence in Charlottesville, when a woman was killed. “There has been a shift for us somewhat on this with the Charlottesville incident,” she said.

The G7 summit is being hosted by the Italian interior minister Marco Minniti. A senior Italian diplomat said: “Some progress has been made in discussing the issue with the internet companies and this needs to continue. It is significant that it has now become a matter for the G7.

“The companies have said they want to help. They have an obligation to do so; they are now international players who have huge influence as well as massive revenue. Last year, for example, Google and Apple became bigger than Exxon and Shell.”

The issue of social media and terrorism is politically sensitive, with human rights groups as well as some internet analysts warning of encroachment on civil liberties if the governments gets unchecked access to content. The online service providers also stress that there needs to be a balance between security and the right to privacy of their clients.

There have been repeated calls from politicians, including Ms Rudd, for access to encrypted material, something which they maintain is needed to detect terrorism-related online activity. However, it appears that security agencies have acquired means to get to some encrypted information.