Prime Minister Narendra Modi expressed grief over the UK Parliament and said that India stands by the country in the fight against terrorism.
The Met Police said that five people, including the attacker, have died and at least 40 were injured in the major terror attack outside the Houses of Parliament on 22 March in London.
"Deeply saddened by the terror attack in London. Our thoughts and prayers are with the victims and their families," tweeted Modi.
"At this difficult moment, India stands with the UK in the fight against terrorism," the prime minister added.
Deeply saddened by the terror attack in London. Our thoughts and prayers are with the victims and their families.— Narendra Modi (@narendramodi) March 23, 2017
Assistant Deputy Commissioner Mark Rowley said that a police officer named Keith Palmer has been killed in the attack. Without giving any details about the attacker, Rowley hinted that he was inspired by international terrorism.
"Also, at this stage, but it may change - we believe approximately 40 people were injured, some with serious injuries, including three police officers, two of whom are in a serious condition," The Guardian quoted Rowley as saying.
"We must recognise now that our Muslim communities will feel anxious at this time given the past behaviour of the extreme right wing and we will continue to work with all community leaders in the coming days," he added.
Earlier, the lockdown in the Westminster attack came to an end, after several hours.
Around 1000 people, including Parliament workers as well as MPs, were locked down in Westminster Abbey. They were interviewed by the police to see if they had any information that could help the inquiry.
Prior to this, at least 20 people, including three officers, were reported hurt when an attacker drove a vehicle into pedestrians on Westminster Bridge, near the Parliament.
One woman was believed to have been thrown over the bridge into the river Thames - and later pulled alive from the water - while another fell onto a hard surface below the bridge.
U.K. Prime Minister Theresa May described the attack as "sick and depraved."
"I have just chaired a meeting of the Government's emergency committee, COBRA, following the sick and depraved terrorist attack on the streets of our Capital this afternoon," she said.
--With ANI inputs