Chandigarh: London mayor Sadiq Khan said on Wednesday that it was time for the British government to formally apologise for the 1919 Jallianwala Bagh massacre, adding it was "shameful" that this had not happened and lending his voice to a long-standing demand of Sikh groups in England and India.

Several British politicians, including former Prime Minister David Cameron, had expressed regret over the massacre, but stopped short of apologising.

Visiting the memorial nearly a century later, mayor Khan wrote in the visitors' book: "It was incredibly moving to visit Jallianwala Bagh. The tragedy in 1919 on Baisakhi is one we must never forget. It is time for the British government to finally apologise. Our thoughts are with all those who died."

"It is wrong that successive British governments have fallen short of delivering a formal apology to the families of those who were killed," said Khan, who is of Pakistani origin.

"I am clear that the government should now apologise, especially as we reach the centenary of the massacre. This is about properly acknowledging what happened here and giving the people of Amritsar and India the closure they need through a formal apology."

Khan, who is from the Opposition Labour Party, does not speak for Britain's Conservative government.

The official Twitter handle of the London mayor later tweeted: "I'm calling on the British government to make a full and formal apology to the people of Amritsar and India for the Jallianwala Bagh massacre. It is shameful that, almost 100 years later, this has not yet happened."

Khan went around the complex near the Golden Temple in Amritsar that houses the Shaheedi Khuh or "martyrs' well", into which protesters fleeing bullets had jumped. Khan saw the bullet marks on the walls surrounding the memorial.

On April 13, 1919, Colonel Reginald Dyer had ordered firing on peaceful protesters and Baisakhi pilgrims assembled at Jallianwala Bagh.

While the then British government put the casualty figure at 379, a plaque at the memorial site states: "This place is saturated with the blood of about two thousand Hindus, Sikhs and Muslims who were martyred in a non-violent struggle."

A hundred years is not late for an apology, as Canadian Prime Minister Justin Trudeau demonstrated in May 2016 when he formally expressed regret in the country's House of Commons for the Komagata Maru incident of 1914.

A Japanese steamship with 376 passengers, mostly Sikh migrants, had not been allowed to dock in Vancouver. On its return to Calcutta's Budge Budge dock, 19 passengers were killed in clashes with the British police.

The British monarchy and the UK government have so far not issued a formal apology over Jallianwala Bagh.

Former Conservative British Prime Minister David Cameron had written in the visitors' book during a visit to Jallianwala Bagh in February 2013: "This was a shameful act in British history, one that Winston Churchill described at that time as 'monstrous'. We must never forget what happened here and we must ensure that the UK stands up for the right of peaceful protests."