Police have since made at least 12 arrests in connection with the attack.
"The rain actually saved us", she said.
Trump said he had spoken with British Prime Minister Theresa May to express America's "unwavering support" and offer US assistance as the British government works to protect its citizens and bring the guilty to justice.
The Islamic State group claimed responsibility for the Manchester bombing, but there was no immediate claim of responsibility for the London attack, which the prime minister linked to Islamic extremism. "It is an ideology that claims our Western values and freedom, democracy and human rights are incompatible with the religion of Islam". Within eight minutes of receiving the first emergency call officers shot and killed the three suspected assailants.
She said the measures were needed because "terrorism breeds terrorism" and attackers copy each other.
"When I open the door I see three dead people on the floor", he said.
The identities of the attackers have not been revealed.
Gerard Vowls, 47, said he saw a woman repeatedly stabbed, and threw chairs, glasses and bottles at the attackers in a bid to stop them.
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"People flee a terrorist attack LIKE LONDONERS #LoveLondon" wrote another.
The attackers, wielding blades and knives, then ran down a set of stairs into Borough Market where they stabbed people in several different restaurants.
"It was horrific", he said.
In another statement on Sunday morning, Khan urged Londonders "to remain calm and vigilant in the days ahead".
And he took an opportunity to defend his own resistance to gun control in the USA, saying: "Do you notice we are not having a gun debate right now? GOD BLESS!" But he also took shots at political correctness and gun control.
"As a country, our response must be as it has always been when we have been confronted by violence: We must come together, we must pull together, and united, we will take on and defeat our enemies".
During the U.S. presidential campaign past year, Mr Trump first proposed the ban on Muslims entering the USA, but suggested he could make an exception for Mr Khan, who is London's first Muslim mayor.
Gov. Gen. David Johnston condemned the attack as "evil", on Twitter.
Whatever the United States can do to help out in London and the U.
Opposition Labour leader Jeremy Corbyn said Britain needed to have hard conversations with Saudi Arabia and other Gulf states about the funding of Islamist extremism. The terror network announced it was behind the deadly attack on a casino and shopping complex in the Philippines last Friday - but Manila police said the killer was a Filipino gambling addict heavily in debt, with no terror links.
"At least 7 dead and 48 wounded in terror attack and Mayor of London says there is 'no reason to be alarmed!'" Trump tweeted. Police later said Masood had no links to extremist groups such as ISIS or al-Qaeda.
A truck plowed into pedestrians on Westminster Bridge in March, and a suicide bomber targeted an Ariana Grande concert in the northern English city of Manchester two weeks ago. Abedi died at the scene.