The Queen has called the London bombings an outrage and urged people to continue their normal lives.
"Those who perpetrate these brutal acts against innocent people should know that they will not change our way of life," she said.
The Queen made the comments as she met survivors of the explosions at the Royal London Hospital in Whitechapel.
She sent her sympathy to all those caught up in the blasts, especially relatives and friends of the victims.
'Respect of all'
Her hospital visit came as Prince Charles and his wife, the Duchess of Cornwall, met staff and survivors at St Mary's Hospital, Paddington.
Royal aides said it was unusual for the Queen to speak so soon after an incident, underlining the gravity of the situation.
The Queen was cheered and applauded as she entered the hospital's canteen to address staff.
In a forthright speech, she said: "Yesterday's bombings in London have deeply affected us all.
"I know I speak for everyone in expressing my sympathy to those who have been caught up in these events and, above all, to the relatives and friends of those who have lost their lives.
"My thoughts are also with the injured, some of whom I have been able to see and talk to today.
"I also want to thank you and all the members of the emergency services and Transport for London who are working with such care, professionalism and sensitivity, often in very difficult condition.
"You have the respect of us all as you go about your business."
The Queen said: "I want to express my admiration for the people of our capital city who in the aftermath of yesterday's bombings are calmly determined to resume their normal lives.
"This is the answer to this outrage. Sadly we in Britain have been all too familiar with acts of terror and members of my generation, especially at this end of London, know that we have been here before.
"But those who perpetrate these brutal acts against innocent people should know that they will not change our way of life.
"Atrocities such as these simply reinforce our sense of community, our humanity and our trust in the rule of law. That is the clear message from us all."
During her 45-minute visit to the hospital, the Queen spoke to Bruce Lait, who suffered a burst eardrum and facial lacerations in the first Tube explosion.
The 32-year-old professional dancer from Ipswich was with his dance partner, Crystal Main, on the way to rehearse for a show when their Tube carriage was ripped apart.
Mr Lait, who was with his parents Pat and Tom, when the Queen visited his bedside.
"I'm very thankful to still be here," he told her, telling the Queen of the devastation caused by the blast, with "glass and flying debris".
"I cannot believe I got away with just this [his injuries]," he said.
The Queen said she hoped Mr Lait would be able to continue dancing once he left hospital.
She asked if he used the Underground a lot and he said: "No. I was just coming down to London to rehearse for a show."
She replied: "Oh, that's cruel, isn't it?"
Mr Lait's mother told the Queen she had not known where her son was until Thursday evening.
The Queen told Mr Lait: "It must have been a great relief when they (his parents) turned up."
Mr Lait replied: "Yes. I had someone to hug."