Labour leader Jeremy Corbyn said he would support calls for May to quit, as she had overseen a sharp reduction in police numbers in her past job as interior minister. "I think the government has to do something".
She wrote: "I called her a lot of times but she never picked up the phone".
The number of police officers in England and Wales fell by nearly 20,000 between 2010 and 2016 - years when May, as home secretary, was in charge of policing.
Of the 48 people taken to the hospital following the violence that started on London Bridge and continued in Borough Market, officials said Monday that "36 are now being cared for in London hospitals with 18 remaining in a critical condition".
Christine Archibald, 30, was among seven who died in a van-and-knife attack on London Bridge and nearby restaurants on Saturday.
At least one other person featured in the documentary has since joined the Islamic State militant group in Syria.
President Trump responded to Saturday's terror attack in London, which left seven people dead, by falsely claiming that the city's mayor, Sadiq Khan, said there was "no reason to be alarmed".
The London mayor, Sadiq Khan, has called on the British government to cancel a planned state visit by Donald Trump after being criticised in two tweets by the U.S. president. Sky News reported on Monday that police had also found Molotov cocktails in the back of the attackers' van.More news: Apple iOS 11 will automatically lock down your phone while you're driving
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Butt had appeared in a television documentary called "The Jihadis Next Door", broadcast a year ago by Britain's Channel 4, one of a group of men who unfurled an Islamic State flag in a park.
White House spokeswoman Sarah Sanders said she did not think it was fair to characterise Trump's tweets as "picking a fight" with Khan, who is the first Muslim elected as London mayor. Several people have come forward saying they reported Mr. Butt to counterterrorism authorities but nothing was done. It is the Islamic duty of every Muslim to be loyal to the country in which they live and we are now asking questions - to understand how extremism and hatred has taken hold within some elements of our own communities.
A Canadian, a French national and a Briton were among the dead, while other French people, a Spaniard, Australians and a New Zealander were among the 48 who were injured in what Prime Minister Theresa May called "an attack on the free world". "It doesn't make any sense", Berry said. The trend has continued since the two attacks, most polls suggest. "We have had to close police stations, sell police buildings and we've lost thousands of police staff". Yesterday, the mayor told Londoners there's no reason to be alarmed by the increased police presence in the city.
All three were ultimately shot and killed by police.
Labour has been targeting cuts to the Home Office's policing budget - the Conservatives have rejected the criticism and a former terrorism law watchdog said linking the cuts to terror attacks was a "completely misleading argument". Butt had been radicalised watching extremist videos online, he said, adding: "We spoke about a particular attack that happened and like most radicals he had a justification for anything and everything, and that day I realised I needed to contact the authorities".
"Your perverse ideology has nothing to do with the true values of Islam".
"To my friends in the United Kingdom: I apologize for this", said Ben Rhodes, a former national security aide to Barack Obama.
"Chrissy was a bright light to many, and her generosity, kind spirit and huge heart for her work in responding to issues of addictions and homelessness at the centre inspired us all".