Online trolls have aimed “vile and upsetting abuse” at victims of the London and Manchester terror attacks, NHS doctors have revealed.

Victims and family members have been targeted on social media, especially Twitter, by trolls who accused them of “cashing in” on the atrocities.

The vitriol received by people wounded in the bomb and vehicle attacks this year was so serious that NHS England has produced guidance warning anyone caught up in a terrorist incident to beware of “unpleasant and abusive” trolls.

Prof Chris Moran, NHS Englnd’s lead for clinical trauma, said: “Social media can play a positive and negative role in the aftermath of a terrorist incident. At the most extreme end, we’ve seen from recent atrocities in Manchester and London that innocent people have unwittingly been the target of trolls who use social media to prey on victims, subjecting them to vile and upsetting abuse.

“These are individuals who are often in a deep state of shock.”

After the Manchester Arena bombing on 22 March, which killed 23 people and injured 250 others, four doctors working with casualties reported at debriefs that victims they had treated or their relatives had been trolled.

Social media can play a positive and negative role in the aftermath of a terrorist incident

NHS England has not released details of the abuse but it is understood that some trolls accused victims of “trying to cash in” on what had happened by talking to the media about their experience.

The perpetrators, who used Twitter, targeted people who had spoken out about the nail bomb attack by Salman Abedi at the Ariana Grande concert and directed messages at victims once their identities were known, NHS sources said.

The experiences in Manchester in particular have prompted NHS chiefs to warn victims of terror attacks, especially young people, to be careful what they say on social media after such an incident in case they unwittingly incite trolling.

Victims should also limit their use of social media and the information they share there in case it brings back painful memories, the NHS says.

The section of the guidance which advises young victims of a terror attack about social media states: “You can also attract trolls: people who draw the most negative conclusions they can, or question your motives that don’t exist or just be plainly unpleasant and abusive, often anonymously too; they can say things like ‘you’re only doing something for money’, or to abuse the system and so on.”

It adds: “This is incredibly hurtful – which is what the sender intends – and it will upset you, or make you angry, and that’s never the best time to think about what you tell [people publicly about their experience or views on something].”

Posting information about a terrorist attack on social media can also worsen the trauma of victims, according to the guidance, which also advises patients and NHS staff on how to deal with journalists after major incidents.

It says: “After an unsettling event try to stay off social media in case you say more than you intend because of what you experienced; messaging your story can keep you in the trauma; retelling your story can also bring back bad memories and can even relive the trauma.”

Those receiving abusive messages should not respond or reply but delete them and block the sender. “Consider reporting hateful and abusive messages to the police and service providers,” it says.

Moran will use a speech at the NHS Expo conference in Manchester next week to set out how social media platforms and conventional publishers can play a beneficial role after a major incident, as well as highlighting the potential downsides, such as trolling.

Prof Neil Greenberg, a spokesman for the Royal College of Psychiatrists, said online abuse could be very damaging to people who were struggling after being caught up in a terrorist attack.

“If someone is still suffering with, for example, PTSD after experiencing a traumatic event, and are trying to get on with their daily lives, then being trolled could lead to their condition deteriorating and them having a setback.

“That could increase their avoidance of social media and reminders of the traumatic event, or make them hyper-vigilant, worsen their concentration and bring up traumatic events in their minds.

“These trolling comments, which are intended to hurt, could stop people moving on from very traumatic events,” said Greenberg, an expert in psychological trauma at King’s College London.

The NHS’s initiative comes as Theresa May has stressed her support for a crackdown on internet bullying and harassment, which has been implicated in a number of cases in which young people have killed themselves.

“If it’s a crime offline, it’s a crime online. I think sometimes people think that online is a different sort of world and it doesn’t matter and you can do what you like. Actually, no, you can’t. You should behave online as you would offline,” the prime minister told the BBC.

Social media users should be educated to understand that their actions online can have consequences in the real world, especially for young people, May said.