The attorney general had previously said the incident "does meet the definition of domestic terrorism."
The Department of Homeland Security and the FBI had warned about vehicle-ramming attacks, but this method is usually associated with Islamist extremists and jihadis.
Monday's attack targeted worshippers from an institution with a proud history of fighting violent extremism.
Figures released by Mayor of London Sadiq Khan show as many as 20 incidents per day.
Khuram Butt and Rachid Redouane were "warned about their conduct" after wrestling in the water.
The divisions in the East End community have turned it into a flashpoint between white nationalists and radical Islamists.
Police have already named the other two attackers as Khuram Butt and Rachid Redouance.
After the third attack in less than three months, Prime Minister Theresa May said Thursday's election would go ahead.
The arrests were made in connection with Saturday's attack that killed seven.
Jewish rebels fought a heroic last stand against the Roman army inside the walls.
In December 2010, an Iraqi-born Swede detonated an explosive device, killing himself.
Safety concerns and test drive accidents are pushing back the date of launch by decades.
The ride-sharing company's pilot program is suspended in Arizona, Pittsburgh and San Francisco pending an investigation.
It is an old Russian strategy to conduct its attacks when the world is looking elsewhere.
Rob Lyon describes how he survived an attack in the heart of British democracy.
The most important metric—miles per intervention—was just 0.8 miles.
Police shoot, injure driver who drove into a crowd standing by a bakery in the town of Heidelberg.
Honda said that the rupture occured in the passenger-side air bag.
The hometown of Franz Kafka had nearly 7 million visitors in 2016.
The Somali attacker had criticized the media for its portrayal of Muslims.