British Muslims, activists and civil rights groups have decried riots in Southport and hate speech in the aftermath of a fatal stabbing attack, as they spoke of a sense of fear and rising Islamophobia.

The northern English seaside town, which was struck by grief after a suspect stabbed children and adults on Monday at a Taylor Swift-themed holiday dance club, was plunged into chaos on Tuesday evening when rioters attacked a local mosque, chanted “F*** Muslims”, and assaulted police.

More than 50 officers were injured during the riots which erupted after a peaceful vigil. Tensions heated up as online misinformation and speculation spread over the knife attack suspect. Unverified claims have suggested he is a Muslim and a migrant.

Police have said the suspect is a 17-year-old who was born in the Welsh capital, Cardiff. He lived in a village near Southport. No further details about him have been announced since suspects cannot be named before they are charged. Furthermore, suspects under 18 have automatic anonymity.

Merseyside Police have said the tragedy, during which Bebe King, six, Elsie Dot Stancombe, seven, and nine-year-old Alice Dasilva Aguiar were killed, is not being treated as a terrorism-related incident.

But figures such as the far-right agitator Tommy Robinson have stirred tensions, railing against Muslims and undocumented migrants after the attack while suggesting the government, police and media are conspiring to hide information from the public.

In a seven-minute video posted on Tuesday to his X account with the caption, “There’s more evidence to suggest Islam is a mental health issue rather than a religion of peace”, Robinson tells his 800,000 followers, “They’re replacing the British nation with hostile, violent, aggressive migrants … Your children don’t matter to [the Labour government].”

Nigel Farage, the hard-right populist MP, shared a video on X on Tuesday in which he asked, “Was this guy (the suspect) being monitored by the security services? Some reports say he was. Others, less sure. Police say it’s a non-terror incident … I just wonder whether the truth is being withheld from us.”

A slew of other accounts on social media sites blamed Muslims for Monday’s attack, which has shocked the United Kingdom and led to an outpouring of grief and sympathy for the families of the victims. Five of the eight other children who suffered stab wounds – and two adults – are in a critical condition.

Merseyside Police said some of the rioters “were believed to be supporters of the English Defence League” – the far-right movement founded by Robinson.

The Liverpool Region Mosque Network said in a statement that it was “shocked and horrified” by the knife attack against children and adults at the dance school.

“A minority of people are attempting to portray that this inhumane act is somehow related to the Muslim community. Frankly, it is not, and we must not let those who seek to divide us spread hatred and use this as an opportunity,” it said.

“I felt terrified for Muslims in Southport,” said Fatima Rajina, a research fellow based at the Stephen Lawrence Research Centre who specialises in issues including identity, race and British Muslims. “No one can ever tell Muslims that our fears are just a figment of our imagination. Islamophobia has always been facilitated by politicians’ dog-whistle politics who’re never held accountable.”

A post on X that has been shared more than 4,000 times, referenced another recent riot that some online agitators mistakenly blamed on Muslims.

“Before you ridicule any British Muslim for saying they no longer feel safe living in the country of their birth, just remember that in the past two weeks, we have been blamed for the Leeds riots and the Southport stabbings, neither of which had anything to do with us,” it said.

In the northern city of Leeds, people recently rioted after local authorities intervened in a child protection case.

The Runnymede Trust race equality think tank said of the Southport riots: “This is the inevitable, devastating, outcome of rising Islamophobia that’s enabled to fester on social media, in mainstream media, and by our political class. Our thoughts are with the people of Southport, and British Muslims across the country.”

The head of the Muslim Council of Britain, Zara Mohammed, said: “At a time of great tragedy, loss, and mourning, we must stand firm against the cynical forces of hatred and division. This does not represent our diverse Britain and the people of Southport. The government must address the increasing rise of violent far-right extremism targeting Muslim communities. More must be done to tackle Islamophobia.”

The Mayor of Liverpool, Steve Rotheram, said the riots “only further traumatise a community that is already struggling to come to terms with this attack. Mindless violence directed at the very people who ran towards the danger yesterday, and outright Islamophobia, only distract from the work of delivering justice.”

Jenni Stancombe, the mother of the seven-year-old victim Elsie Dot Stancombe, called for calm.

“This is the only thing that I will write, but please stop the violence in Southport tonight,” she posted on social media.