LONDON (AFP) - Hundreds of people joined hands in a human chain in the heart of London on Wednesday (March 29) to pay tribute to the four people killed in a terror attack a week ago.

The mourners also observed a minute's silence at the very moment on March 22 when Khalid Masood ploughed his car into a crowd in a rampage that killed three people on Westminster Bridge in the shadow of Big Ben.

He then stabbed a police officer at the entrance of the Houses of Parliament to death before being shot dead by armed police.

Many gathered on the bridge were Muslims, there to pay tribute to the victims and to distance themselves from the 52-year-old Masood, who had converted to Islam.

"Islam says NO to terror" and "Islam means PEACE", said some of the placards.

"We will not turn against each other and we will challenge those that seek to divide us," said Mustafa Field, head of the Faiths Forum for London charity.

Mak Chishty, a police commander who took part in the vigil, said he felt "very emotional, very sad, very shaken".

Around 50 people were also injured in the attack and 12 remain in hospital after the attack which the Islamic State said was carried out by one of its "soldiers".

Police arrested 12 people in total over the killings but only two remain in custody on suspicion of "preparation of terrorist acts".

Parliament speaker John Bercow said there would be two reviews into security after Masood managed to gain access to the courtyard of the building.