A long-serving member of Parliament was stabbed to death Friday during a meeting with constituents at a church in England, in what police said was a terrorist incident. A 25-year-old man was arrested in connection with the attack, which united Britain’s fractious politicians in shock and sorrow.

Counterterrorism officers were leading the investigation into the slaying of Conservative lawmaker David Amess. In a statement early Saturday, the Metropolitan Police described the attack as terrorism and said the early investigation “has revealed a potential motivation linked to Islamist extremism.”

Amess, 69, was attacked around midday Friday at a Methodist church in Leigh-on-Sea, a town about 40 miles (62 kilometers) east of London. Paramedics tried without success to save him. Police arrested the suspect and recovered a knife.

Also read: UK lawmaker stabbed in eastern England has died

They did not identify the suspect, who was held on suspicion of murder. Police said they believed the suspect acted alone, and were not seeking anyone else in connection with the killing, though investigations continue.

The slaying came five years after another MP, Jo Cox, was murdered by a far-right extremist in her small-town constituency, and it renewed concern about the risks politicians run as they go about their work representing voters. British politicians generally are not given police protection when they meet with their constituents.

Read: Shooting in Russian university leaves 8 dead

Tributes poured in for Amess from across the political spectrum, as well as from the community he had served for decades. Residents paid tribute to him at a vigil at a church in Leigh-on-Sea.

“He carried that great East London spirit of having no fear and being able to talk to people and the level they’re at,” the Rev. Jeffrey Woolnaugh said at the vigil, attended by about 80 people. “Not all politicians, I would say, are good at that.”

Conservative Prime Minister Boris Johnson said he and his Cabinet were “deeply shocked and heart-stricken.”

“David was a man who believed passionately in this country and in its future, and we’ve lost today a fine public servant and a much-loved friend and colleague,” Johnson said.

The prime minister would not say whether the attack meant politicians needed tighter security, saying, “We must really leave the police to get on with their investigation.”

Amess had been a member of Parliament for Southend West, which includes Leigh-on-Sea, since 1997, and had been a lawmaker since 1983, making him one of the longest-serving politicians in the House of Commons.

A social conservative on the right of his party, he was a well-liked figure with a reputation for working hard for his constituents and campaigning ceaselessly to have Southend declared a city.

Amess, who leaves a wife and five children, was knighted by Queen Elizabeth II in 2015 for his service, becoming Sir David.

Flags at Parliament were lowered to half-staff amid a profusion of questions about lawmakers’ security.

“This is an incident that will send shockwaves across the parliamentary community and the whole country,” House of Commons Speaker Lindsay Hoyle said. “In the coming days we will need to discuss and examine MPs’ security and any measures to be taken, but for now, our thoughts and prayers are with David’s family, friends and colleagues.”

Violence against British politicians is rare, but concerns have grown about the increasingly bitter polarization of the country’s politics.

In 2016, a week before the country’s divisive Brexit referendum, Cox, a Labour Party lawmaker, was fatally stabbed and shot in northern England. Also, several people have been jailed in recent years for threatening lawmakers.

British lawmakers are protected by armed police when they are inside Parliament, and security there was tightened after an attacker inspired by the Islamic State group fatally stabbed a police officer at the gates in 2017.

But politicians have no such protection in their constituencies. Amess published the times and locations of his open meetings with constituents on his website.

Two other British lawmakers have been attacked over the past two decades during their “surgeries,” regular meetings where constituents can present concerns and complaints.

Labour legislator Stephen Timms was stabbed in the stomach in 2010 by a student radicalized by online sermons from an al-Qaida-linked preacher.

In 2000, Liberal Democrat Nigel Jones and his aide Andrew Pennington were attacked by a man wielding a sword during such a meeting. Pennington was killed and Jones wounded in the attack in Cheltenham, England.

Former Prime Minister Theresa May, a Conservative, tweeted that Amess’ killing was a “tragic day for our democracy,” and former Labour Prime Minister Tony Blair said he was “shocked and horrified.”

Scottish First Minister Nicola Sturgeon of the Scottish National Party said on Twitter: “In a democracy, politicians must be accessible and open to scrutiny, but no one deserves to have their life taken while working for and representing their constituents.”

Kim Leadbeater, Jo Cox’s sister and now a member of Parliament herself, said it was “horrific” that Amess’ family was experiencing what hers had gone through.

“They will think about this every single day for the rest of their lives,” she said.

“I find myself now working as a politician and trying to do good things for people, and it’s really important you get good people in public life, but this is the risk we are all taking, and so many MPs will be scared by this.”