In London, the Big Ben and London Eye were lit up in red to honour the victims of the attack
In Paris, the lights of the Eiffel Tower were turned off at midnight. The city's mayor Anne Hidalgo said the two capitals "share a common love of freedom and an attachment to democracy" and were "tolerant and cosmopolitan cities, open to the world."
In Tel Aviv, the city hall was lit up in the colours of the Union Jack flag. Tel Aviv's mayor Ron Huldai tweeted this picture
The British city of Birmingham lit up its library in red, white and blue - the colours of the British flag
Closer to home, sand artist Sudarsan Pattnaik tweeted this picture of a sand sculpture condemning the attack from Odisha's Puri beach
On Twitter, the hashtags #WeAreNotAfraid, #LondonStrong and #PrayForLondon began trending after the attack at Westminster.
London will react today the way it always does to terror attacks. Pick itself up, dust down, and just get on with it. #LondonStrong— Mark Donovan (@markydonovan) March 22, 2017
No place for terrorism, only tea.#WeAreNotAfraid— Rav Vadgama (@TVRav) March 22, 2017
And proving the city would not cower down in the face of terror, London Underground staff used message boards that usually give information about the running of the tube to broadcast thoughtful messages of peace and resilience
Today, British police arrested seven people in armed raids for Wednesday's deadly attack.