British police were providing “reassurance patrols” around mosques following the deadly gun rampage in New Zealand on Friday.
London’s Mayor Sadiq Khan and Britain’s top counter-terror officer said the police presence would be stepped up as people went to Friday prayers.
“I want to reassure the Muslim communities in London,” said Khan.
“I have been in touch with the Met Police. There will be highly visible policing around mosques today, as well as armed response officers, as Londoners go to pray.”
Neil Basu, the Met’s national policing chief for counter-terrorism, said: “We will be stepping up reassurance patrols around mosques and increasing engagement with communities of all faith, giving advice on how people and places can protect themselves.
“Together with our intelligence partners we continually monitor the varied threats we face, including to and around places of worship and specific communities across the country,” he said.
Harun Khan, head of the Muslim Council of Britain said British Muslims preparing for Friday prayers “do so with the anxiety as to whether our mosques and communities are safe in the face of unabated Islamophobia and hostility against Muslims”.
The MCB said two mosques in Newcastle and Manchester had been targeted by vandals who spray-painted Nazi swastika symbols in the past two months.
London has previously heightened security measures around mosques following terror attacks.
Extra patrols were deployed after the Finsbury Park attack on 19 June, 2017.
Attacker Darren Osborne drove a van into pedestrians leaving a Muslim welfare centre near the well-known Finsbury Park Mosque in north London.
One person was killed and several others were injured.
Osborne was arrested at the scene and sentenced to life imprisonment.
Basu said British counter-terror officers were ready to support their colleagues in New Zealand in responding to and investigating Friday’s attack.
An extremist armed with semi-automatic weapons rampaged through two mosques in the New Zealand city of Christchurch during afternoon prayers Friday, killing 49 worshippers and wounding dozens more.
Basu said places of worship could use an online training package for advice on protective security and how to respond in case of an incident.