British police closed a road in central London near British Prime Minister Boris Johnson's official residence on Monday.
The police said they had arrested a man armed with a knife who had confronted two Ministry of Defence police officers, reports Reuters.
Whitehall, which is home to several government departments including the finance ministry, Foreign Office and Ministry of Defence and leads to Johnson's Downing Street office and residence, was cordoned off by police.
Police said they had launched an investigation following the incident at Horse Guards Parade, a ceremonial parade ground that overlooks St James's Park.
"At around 08:50hrs, a 29-year-old man, who was armed with a knife, confronted two Ministry of Defence Police officers. The man was restrained by officers. There were no reports of any injuries," London's Metropolitan Police said in a statement.
"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."