The CEO of Twitter, Dick Costolo has revealed that he and his staff have received death threats from terror group ISIS.

The social media site became a target for the militant group after the accounts being used by the terrorist organization were shut down.

Twitter has been used by the extremist organisation as a form of propaganda for enlisting new recruits and to promote ISIS activities.

Users linked to the extremists tweeted a series of messages urging 'lone wolves' in the US and Europe to take decisive and deadly actions against their target.

A specific warning was directed at staff at the Silicon Valley headquarters, warning they would 'bring the war' to San Francisco.

One of the calls is believed to have come from Al Musra Al Maqdisia, or The Supporters of Jerusalem - a Jerusalem-based group that pledged its allegiance to ISIS in February.

The tweets from the now-suspended account read: "#TheConceptOfLoneWolfAttacks The time has arrived to respond to Twitter's management by directly attacking their employees and physically assassinating them!! Those who will carry this out are the sleepers cells of death."'

"Twitter management should know that if they do not stop their campaign in the virtual world, we will bring the war to them in the real world on the ground."'

The user then directly threatened workers at the Silicon Valley headquarters: "Every Twitter employee in San Francisco in the United States should bear in mind and watch over himself because on his doorstep there might be a lone wolf assassin waiting."

And finally, they urged Europe to join the pledge: "#AttackingTwitterEmployees is on the agenda of mujahedeen and lone wolves who are across Europe."

Reacting to the threats, Mr Costolo said: "After we started suspending their accounts, some folks affiliated with the organization used Twitter to declare that employees of Twitter and their management should be assassinated. Obviously that's a jarring thing for anyone to deal with," the CEO added.

Speaking at the government intervention at the Vanity Fair New Establishment Summit in San Francisco, Mr Costolo said: "Whenever you have a global public information-sharing channel, you are going to have people that use it for good. It's obviously been a tool for social change, beneficial social change in a number of countries around the world.

Commenting on those who use the micro media site to disseminate sensitive and offensive information he said: "It's against our terms of service. It's against the law in many of the countries in which we operate for them to use it to promote their organization. And when we do find those accounts we shut them down. We shut them down quite actively."

The social network has been a crucial platform for the jihadis to promote their objectives and their actions, creating Twitter storms, spamming the site with their beliefs and calling on Western recruits to join them.