Soldiers who had been drafted in to guard public sites in order to free up police resources will "return to their original positions" over the next few days, Ms Rudd said.
The two suspects - one is 18 and the other is 21 - were arrested by British police on Saturday.
U.K. Home Secretary Amber Rudd said speculation by U.S. President Donald Trump over Friday's commuter train bombing in west London is unhelpful while police continue to investigate the attack.
The second arrest comes after an 18-year-old - the youngest to be arrested over a terror attack in the United Kingdom - was quizzed by cops after he was seized in Dover. "We have no evidence to suggest that yet".
He said: "The high pace and rapid progress of this investigation is continuing".
Two men are now in custody for possible roles in the bombing attack on a rush-hour subway train Friday that injured 29 people in London.
Police had earlier searched a house in Sunbury believed to be linked to the first suspect, who was arrested at the Dover ferry port.
The couple, Ronald Jones, 88, and his wife Penelope, 71, who were honoured for services to children and families, are said to be staying with friends following the police raids.
Jim Adaway, a family friend, said the Joneses recently returned to foster caring to help resettle youngsters from overseas.
"All I know is that they gave up the fostering and someone got in touch with them and they started taking kids again, refugees, about a year ago".
"I think Penny was getting in touch with (the authorities) saying "I can not handle this one".
Thirty people were injured when an improvised explosive device caused a fireball on a District Line carriage.
Counter-terrorism officers are leading the investigation supported by MI5. You will see more police - including armed officers - on the streets and transport network throughout the week.