London police arrested a second man in connection with an incident at Buckingham Palace that detectives are calling a terror attempt.
The second suspect, a 30-year-old man, was detained Sunday in west London on "suspicion of being involved in the commission, preparation or instigation of terrorism."
Previously, police said they believed the first suspect had acted alone.
A man armed with a 4-foot sword was detained after deliberately driving a car toward police outside Buckingham Palace on Friday night.
"Uniformed officers then confronted the driver of the vehicle and during that confrontation the driver reached for a 4-foot sword" in the car, said Dean Haydon, commander of the Metropolitan Police counterterrorism branch.
Haydon said the suspect repeatedly shouted "Allahu akbar!" ("God is great" in Arabic) during the confrontation. Three London police officers were injured in a struggle with the suspect, but only two required medical treatment for minor cuts.
Police said they believe the 26-year-old suspect was acting alone, but counterterror officers conducted a series of searches in Luton, north of London, where the suspect is from.
"While we cannot speculate on what the man was intending to do - this will be determined during the course of the investigation - it is only right that we investigate this as a terrorist incident at this time," Haydon added.
British media reported that no members of the royal family were in Buckingham Palace at the time.
Both British Prime Minister Theresa May and London Mayor Sadiq Khan thanked police for acting quickly.
I want to thank the officers who acted quickly and bravely to protect the public last night... 1/2— Theresa May (@theresa_may) August 26, 2017
...demonstrating the dedication and professionalism of our police. 2/2— Theresa May (@theresa_may) August 26, 2017
The Associated Press contributed to this report.