The man suspected of mowing down a crowd exiting Ramadan prayers at a London mosque early Monday has been identified as 47-year-old Darren Osborne of Cardiff, Wales, sources told Sky News.

At least one person was killed and 10 others were injured in the assault, which authorities were treating as a terrorist attack.

Osborne, reportedly a father of four, was arrested on suspicion of terror offenses in the collision with pedestrians outside the Muslim Welfare House, Metropolitan Police said. People at the scene shouted at him: "Why did you do that? Why?"

"This man was not known to authorities in the space of extremism or far-right extremism," Ben Wallace, Britain's minister for security, told Sky News.

The incident occurred outside the Finsbury Park Mosque shortly after midnight after Ramadan prayers. Police said all of the injured were members of the Muslim community. Muslim leaders decried the collision as a hate crime and asked the public to stay calm.

Police said eight of the injured were taken to three hospitals and two suffered minor injuries and were treated at the scene.

Witnesses reported seeing at least one person receiving chest compressions. Police said that person was the lone death in the incident, but it was unclear if it was the van that caused the death.

Prime Minister Theresa May described the attack as a "sickening" attempt to destroy liberties that unite Britain, such as freedom of worship. She added that the man acted alone. May said earlier she would chair an emergency security Cabinet session later Monday and that her thoughts were with the injured, their loved ones and emergency officials who responded to the incident.

The Department of Homeland Security (DHS) has responded to the attack and said the Secretary of Homeland Security, John Francis Kelly, has been briefed.

“DHS stands with our European allies in fighting back against all forms of terrorism, and we will continue to work together to keep our communities safe against violent extremists who target any of our people,” a statement by the DHS said.

“Our thoughts and prayers are with all affected by these violent and reprehensible attacks.”

A leader of the Muslim Council of Britain called for extra security at mosques in light of the apparent attack. The group's general secretary, Harun Khan, described the incident as a hate crime against Muslims.

"During the night, ordinary British citizens were set upon while they were going about their lives, completing their night worship," he said. "It appears from eyewitness accounts that the perpetrator was motivated by Islamophobia."

London Mayor Sadiq Khan, the first Muslim to serve in that position, said extra police would be deployed. He called the incident a "horrific terrorist attack." 

Khan also called on Britain's government to supply more funding and resources to the city's police force.

"My message to the Government is  - we need to get the right of level of funding for a capital city," Khan said in a news conference. 

Video filmed in the immediate aftermath showed a Caucasian man being detained by police. 

Imam Mohammed Mahmoud, who reportedly stopped the suspect from being harmed by a group of angry people, said he and others did their best to calm tensions. 

"We extinguished flames of anger or mob rule that would have taken charge," Mahmoud said.

The chairman of the Finsbury Park Mosque said the van crash that hit worshippers was a "cowardly attack" and urged Muslims going to mosques to be vigilant.

Mohammed Kozbar said the Muslim community is "in shock." He complained that the "mainstream media" was unwilling to call the attack a terrorist incident for many hours.

London police closed the area to normal traffic. A helicopter circled above the area as a large cordon was established to keep motorists and pedestrians away.

Witnesses told British media that the van seemed to have veered off the road and hit people intentionally. They also said two men jumped out of the van and fled the scene, but police said the suspect was only one man and the investigation is still ongoing.

Mohammed Shafiq of the Ramadhan Foundation, a Muslim organization, said that based on eyewitness reports, it seems to be a "deliberate attack against innocent Muslims."

Labour Party leader Jeremy Corbyn said in a tweet he was shocked by the incident.

Britain's terrorist alert has been set at "severe," meaning an attack is highly likely.

The Associated Press contributed to this report.