Chishty said: "We have had three attacks across the United Kingdom in three months which requires a step change - a different direction and a different movement to counter the scourge of terrorism, extremism and hatred that we have in our communities at present".
London police on Sunday evening said commuters could expect to see more officers on the streets and more physical measures on bridges, after at least three men killed seven people at London Bridge on Saturday.
"The mayor is focused on dealing with Saturday's horrific and cowardly attack and working with the police, the emergency services and the Government to keep London safe".
Butt, 27, was a British citizen born in Pakistan and married with children, according to police.
He once featured in a Channel 4 documentary about extremists with links to the banned group al-Muhajiroun. Rachid Redouane, 30 (31.7.86) had claimed to be Moroccan and Libyan. Ten people are now in custody.
The white Renault van used in the attack was recently hired by one of the attackers, police added. "And so, we have to guard our freedoms, but we have to understand that for a certain time, we're going to have to compromise them, as well".
"No reason to be alarmed". After taking a selfie on the bridge, he walked away. "We will defeat you".
There was no immediate response from Khan to Trump's latest Tweet. Of those, 21 are still in a critical condition.
The armed responding officers fired more than 50 rounds at the three attackers; one bystander was struck by a bullet but is expected to recover.
The Met said that family liaison officers had been deployed to support the families of the victims killed in Saturday's attack. The policy has been controversial and May's Labour opponent in the coming elections, Jeremy Corbyn, opposed it in 2015.
Campaigning resumed on Monday after being suspended for a day.
The news raises questions about the police's judgment and increases pressure on Prime Minister Theresa May, who three days before a national election is facing criticism for overseeing cuts to police during her years as interior minister.
May, under fire because of three major attacks in Britain in the last three months, said Corbyn wasn't fit to safeguard Britain's security at a time of heightened threat.
May has said counter-terrorism budgets have been protected and the police were given the powers they need.
The sister of a missing 32-year-old man said Monday her brother is believed to have died in the attack.