May said police saved "countless lives" by killing the three London bridge attackers within eight minutes on Saturday night.
They were shot dead in a hail of police gunfire.
British counterterrorism investigators searched homes and detained more people Monday in the London attack investigation as an intense political firestorm developed over Prime Minister Theresa May's role in reducing police ranks.
The 12 people arrested on Sunday in connection with the investigation have been released without charge, police said today.
Meanwhile, the first victim of the attack has been named as Canadian national Chrissy Archibald.
A statement from her family said she "believed strongly that every person was to be valued and respected".
Asked whether she regretted presiding over the cuts, May did not answer the question, saying London's Metropolitan Police was well resourced and had powerful counter-terrorism capabilities.
Michael Mimbo, 25, who spoke to AFP on his doorstep in a neighbouring apartment complex, said the attacker was "an Asian male" - a term used in Britain to refer to people from or with origins in the Indian subcontinent.
He said no action was taken.
"I don't know enough about it yet", the Pentagon chief said, adding, "I like learning about something before I talk".
Three police vans and around a dozen officers could be seen outside.
Both London Bridge rail and Tube stations will reopen on Monday from around 05:00 BST but the rail station will be exit only until at least 08:00 BST. Salman Abedi, who murdered 23 people at an Ariana Grande concert at the Manchester Arena last month, was said to have been reported to authorities on five separate occasions in five years.
On Monday May emerged from a meeting of the government's emergency Cobra committee and said: "Enough is enough". She said it was "time to say enough is enough" and end the UK's "tolerance" of extremism.
"While our pain will never diminish, it is important for us all to carry on with our lives in direct opposition to those who wish to destroy us and remember that hatred is the refuge of small-minded individuals and will only breed more".