A man was arrested on suspicion of attempted murder after confronting police with a knife in Westminster.
The suspect approached the two Ministry of Defence (MoD) police officers with the weapon on Horse Guards Parade at around 8.50am.
The man had to be Tasered and was then restrained by officers. He was arrested on suspicion of attempted murder and possession of an offensive weapon.
There were no reports of any injuries. He remains in custody at a central London police station, the force said. Police confirmed that the incident is not being treated as terror-related.
The Metropolitan Police have launched an investigation into the incident and said it will liaise closely with the MoD police as it progresses.
A number of forensic officers were spotted at the scene putting items into plastic bags as they swept the area for evidence.
Numerous roads were closed in Whitehall and a police cordon was put in place between Trafalgar Square and Parliament Square.
Roads opened to traffic and pedestrians at around 2.30pm and the police cordon was removed.
Horse Guards Parade is the location of a number of government buildings, including the MoD, and is only a short distance from No 10 and the Cabinet Office.
A Met spokesperson said: “An investigation has been launched following an incident at Horse Guards Parade in Westminster on Monday morning.
“At around 08.50, a 29-year-old man, who was armed with a knife, confronted two Ministry of Defence police officers.
“Taser was deployed and the man was restrained by officers. There were no reports of any injuries.
“He was arrested on suspicion of attempted murder and possession of an offensive weapon and remains in custody at a central London police station.
“The incident is not being treated as terror-related.
Police are appealing for anyone who may have witnessed the incident or otherwise has information to call 101, providing the reference 1730/18APR.
Information can also be provided to Crimestoppers, anonymously, on 0800 555 111.
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