LONDON — Police arrested a man on suspicion of attempted murder after he entered the London Central Mosque on Thursday afternoon and allegedly stabbed the muezzin, who makes the call to prayer.

The victim’s injuries are not life-threatening, police said. The man, who is in his 70s, was treated by emergency medical technicians at the scene and was taken to a hospital.

Ayaz Ahmed, an adviser for the mosque who witnessed the attack, told the Guardian that worshipers had just begun to say the afternoon prayers about 3 p.m. The suspect was behind the muezzin and then allegedly stabbed him, Ahmed said.

“We all tussled with him, a few hundred people were worshiping at the time. The muezzin has been here for 25 years, calling the prayer five times a day, he is very respected,” he said.

The suspect was apprehended by worshipers and held until police arrived, according to a statement from the mosque.

Photos posted on social media showed police officers holding down and handcuffing a man wearing a red hoodie who was sprawled on the blue carpet.

Police did not release the suspect’s name, and a possible motive and affiliation were not yet known. Police did not label the stabbing a terrorist attack.

“A 29-year-old man, who is believed to have been attending prayers, was arrested inside the mosque on suspicion of attempted murder,” the Metropolitan Police said in a statement.

“The incident is not being treated as terror-related at this time,” police added.

Imam Chokri Majouli discounted the possibility that the attack was racially motivated. In an interview posted on social media, the imam said the suspect often prayed at the mosque and seemed to have a mental illness. He said the man sometimes prayed off to the side while smiling to himself.

Said Ahmed: “I heard the scuffle, the muezzin yelled and screamed, the imam ended the prayer. It was 30 seconds of mayhem. He was stabbed on the right side of his neck. . . . Everybody’s reaction was shock and horror, the men were screaming. It was a vicious attack.”

British Prime Minister Boris Johnson tweeted that he was “deeply saddened to hear of the attack at the London Central Mosque. It’s so awful that this should happen, especially in a place of worship. My thoughts are with the victim and all those affected.”

Just a few hours before the attack in London, Johnson also expressed support for Germany after a gun rampage in the town of Hanau left 11 people dead. “The UK stands with our German friends against this racist assault on our values,” he said.

London has been the scene of a string of attacks by both Islamist terrorists and white nationalist extremists.

In 2017, a 47-year-old man plowed a van into a group of evening worshipers outside a mosque in Finsbury Park. A 51-year-old man was killed and nine others were injured. The perpetrator, Darren Osborne, received a life sentence. The judge said that Osborne had been radicalized over the Internet by those “determined to spread hatred of Muslims.”

Although authorities did not connect Thursday’s attack to terrorism, British Muslims expressed fears.

One social media user, who posted photos on Thursday, wrote: “This is absolutely terrible. No muslim is safe in their places of worship!!”

London Mayor Sadiq Khan, who is Muslim, tweeted, “Every Londoner is entitled to feel safe in their place of worship & I want to reassure London’s communities that acts of violence in our city will not be tolerated.”

The London Central Mosque, also known as the Regents Park Mosque and the Islamic Cultural Centre, is an iconic landmark, with its large golden dome, located in the heart of central London. Nearby are embassies, museums and the official residence of the U.S. ambassador to Britain.

The land for the mosque was donated to Britain’s Muslim community by King George VI in the 1940s. The landmark complex was not completed until the late 1970s.

Azhar AlFadl in Washington contributed to this report.