ISIS declares war on Twitter: Terror group warns employees they will be assassinated for closing down Islamist propaganda accounts

Jerusalem-based group connected to ISIS tweeted threat to Twitter
Called on 'lone wolves' to assassinate employees for closing accounts
Issued specific warning to staff at headquarters in Silicon Valley
The social media site is a key platform for the group's propaganda

An ISIS-affiliated group has threatened to assassinate Twitter employees that close down their accounts.

Users linked to the extremists tweeted a series of messages on Sunday urging 'lone wolves' in the US and Europe to make the firm their target.

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

Threat: Twitter employees at the San Francisco office have been threatened with death for closing accounts

The warning came from the now-suspended account of Al Musra Al Maqdisia, an ISIS-linked group in Israel

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, translated by Vocativ, 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.'

It continued: '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'.

The social network has been a crucial platform for the jihadis to promote their warped interpretation of Sharia law.

The freedom of speech premise that underlies Twitter makes regulation of extremist propaganda almost impossible.

Clampdown: Twitter has worked to shut down any accounts sharing details of Steven Sotloff's assassination

Tweeting: Salma Halane (left) and her twin Zahra (right), from Manchester, have been tweeting from Syria

Tactics have included Twitter storms, spamming the site with their beliefs and calling on Western recruits to join them.

Many of the British and American jihadis that have fled their native countries to join the faction in Iraq and Syria have been tweeting their experiences.

An 18-year-old British girl yesterday tweeted 'I want David Cameron's head on a spike' in a slew of ISIS messages.

One of the twins from Chorlton that fled to join ISIS in Syria has been tweeting messages to the UK, mocking concerns for their welfare.

Either Salma or Zahra Halane has taken the name Umm Ja'far and tweeted a slew of fanatical messages, including several revealing she still plans to be a doctor - but only so she can treat ISIS fighters.

Attacks: ISIS has taken a mass of land the size of the United Kingdom across Syria and Iraq

She wrote: 'I love the name Terror Twin because it makes me sound scary. Isis love it when they make us sound scary because it makes us a big threat so I love it.'

She added: 'I support the executions of Syrian soldiers. It's self defence.'

However, in the wake of the murders of James Foley and Steven Sotloff at the hands of ISIS, the firm has worked to shut down accounts that permeate the organisation's message.

Now, the group is reacting.

Twitter has bureaus across the world.

There are 12 in the US, including the headquarters, and five in Europe.

A further two are in Latin America, three in Asia, one in Australia and two in Canada.

A Twitter spokesman said: 'Our security team is investigating the veracity of these threats with relevant law enforcement officials,'

Shocking footage of ISIS militants as they march onto Baghdad