LONDON — London officials are telling visitors that the city remains a safe and welcoming destination in the wake of yesterday’s horrific attack, which city leaders are denouncing as a terrorist attack.

“I want to reassure all Londoners, and all our visitors, not to be alarmed,” said Mayor Sadiq Khan, yesterday after the attack that left several people dead and dozens injured including tourists from France, China and the U.S. “Our city remains one of the safest in the world.”

Security was heightened last night as extra armed and unarmed police officers patrolled in the streets “in order to keep Londoners, and all those visiting our city, safe,” said Khan.

Britain’s Parliament observed a minute of silence today to remember the police officer and two civilians killed a day earlier in the attack at the heart of London, while authorities raided homes in central England to search for evidence.

Eight people were arrested in raids, including some in Birmingham. Police searched for clues as to why a man driving an SUV plowed into pedestrians on Westminster Bridge, killing two and injuring more than 30 others, before he fatally stabbed a police officer on Parliament’s grounds. Police shot and killed the attacker.

Parliament was locked down for several hours, and the adjoining Westminster subway station was shuttered. Many visitors were on the London Eye when the attack occurred, and it was briefly on lockdown.

A candlelit vigil is taking place tonight at Trafalgar Square in solidarity with the victims and their families, and to show that London remains united, says Khan.

“London is the greatest city in the world and we stand together in the face of those who seek to harm us and destroy our way of life. We always have and we always will. Londoners will never be cowed by terrorism.”

With file from The Associated Press.