LONDON: Twenty protesters have been arrested by the British police after a Sikh demonstration outside Indian Embassy against alleged police brutality in Punjab turned violent, leaving one policeman injured.

Hundreds of demonstrators of a group called ' Sikh Lives Matter ' gathered for a sit-in protest yesterday against the alleged police brutality against Sikhs in Punjab, but the initially peaceful demonstration turned violent forcing police to cordon off the area around the Indian mission in central London.

READ ALSO: Punjab protests ebb, but Sikh clergy in turmoil

The police said they were aware of a "planned demonstration" at Indian High Commission but were forced to take action as the protesters blocked roads causing disruption.

"Whilst it was initially a peaceful protest, the demonstrators blocked the roadway at the Aldwych and caused significant disruption to the central London road network," the Metropolitan Police Service said in a statement .

"Police liaison officers attempted to negotiate with those present, in order to facilitate peaceful protest and minimise the disruption to the public," it said.

"Additional officers, including those from the Mounted Branch, were mobilised to the area and a small group of protesters became violent towards police," the statement added.

During the altercation, one police officer suffered a head injury and was taken to hospital. No other persons were reported to be injured, they said.

At this stage police believe a number of offences may have been committed.

"There have been 20 arrests - the majority of which have been for affray," it added.

READ ALSO: Punjab books unnamed cops for 'murder' over protest deaths

"The point of the protest was to raise awareness and show the Indian authorities that Sikhs of the UK stand in solidarity with the community in the Punjab who are suffering at the hands of Indian authorities," said Jasveer Singh Gill, a spokesperson of the Sikh PA who was present at the spot.

Commercial and educational establishments were affected and transport services disrupted in parts of Punjab last week in response to a bandh called by Sikh outfits against the killing of two youths and police action during protests over alleged desecration of their holy book.