Forensic officers work at the scene of a terror attack at London Bridge in London on Sunday, June 4. At least seven people were killed in attacks late Saturday as a van mowed down pedestrians on London Bridge before attackers then stabbed victims at nearby Borough Market. DANIEL LEAL-OLIVAS/AFP/Getty Images

Counterterrorism officers patrol near the scene of the attack on London Bridge. When speaking to the media on Sunday, British Prime Minister Theresa May did not announce any increase in the UK terror threat level. Dan Kitwood/Getty Images

A woman reacts after asking a Police officer to lay flowers near London Bridge as a tribute to the victims of the attack. DANIEL LEAL-OLIVAS/AFP/Getty Images

UK police officers on Sunday continue their investigation into the terror attacks on London Bridge and in a nearby restaurant district. The attacks on June 3 came days before a general election and two weeks after 22 people were killed when a suicide bomber targeted an Ariana Grande concert in Manchester. DANIEL LEAL-OLIVAS/AFP/Getty Images

Prime Minister Theresa May makes a statement at 10 Downing Street, following a Cobra security meeting in response to Saturday night's terror attack. Violence must "never be allowed to disrupt the democratic process," May said, adding that Thursday's general election will go ahead. Leon Neal/Getty Images

Abandoned buses line London Bridge as the scene remains under investigation following the attack. Metropolitan Police Assistant Commissioner Mark Rowley said in a statement Sunday that a white van struck pedestrians on London Bridge. Attackers then left the vehicle and "a number of people were stabbed, including an on-duty British Transport Police officer who was responding to the incident at London Bridge," said Rowley. The officer received serious but not life-threatening injuries. Dan Kitwood/Getty Images

Counter terrorism officers move up an escalator under The Shard, an iconic highrise near the scene of last night's London Bridge attack. Dan Kitwood/Getty Images

A group of police forensic officers walks in the street outside Borough Market. PA Images/Sipa

People lie on the ground after being detained by police at Elizabeth Fry apartments in Barking, east London, which officers raided Sunday, June 4, following Saturday's terror attack at London Bridge and Borough Market. Furqan Nabi/AP

A bouquet of flowers left near the police cordon at London Bridge on June 4. DANIEL LEAL-OLIVAS/AFP/Getty Images

A view from above shows where a van struck pedestrians on London Bridge -- and then crashed into a barrier. Sanya Burgess/The Sunday Times

This image, from London's Borough Market, shows two of the attackers after they were shot by London police. The attackers drove a white van into pedestrians on London Bridge, leaving bodies lying in the roadway, a witness to the incident told CNN Gabriele Sciotto

Armed police patrol near London Bridge on Saturday, June 3. Mayor Sadiq Khan said it was a "deliberate and cowardly attack" on Londoners enjoying Saturday night out. Dominic Lipinski/PA via AP

The white van used in the attack is seen near London Bridge. Courtesy Universal News and Sport

Police carry out a search near empty buses on London Bridge, Saturday, June 3. Rob Pinney/London News Pictures/Zuma

A person is treated for injuries near London Bridge. Ben Cawthra/REX/Shutterstock

Members of the public flee after reports of the incident involving a vehicle and pedestrians. Ben Cawthra/REX/Shutterstock

Police and emergency responders attend to an injured person. DANIEL SORABJI/AFP/Getty Images

An armed Police officer gestures after the attack in central London. Dominic Lipinski/AP

Guests from the Premier Inn Bankside Hotel are evacuated following the attacks. Yui Mok/PA Wire via AP

A woman wearing an emergency blanket talks on her phone at London Bridge train station. London Bridge Tube station was closed and London Bridge was closed in both directions. CHRIS J RATCLIFFE/AFP/Getty Images

Armed police raid The Blue Eyed Maid on Borough High Street. Carl Court/Getty Images

Debris and abandoned cars remain at the scene of one of the incidents. CHRIS J RATCLIFFE/AFP/Getty Images

Police sniffer dogs are seen at London Bridge. Dominic Lipinski/PA Images via Getty Images

A helicopter flies near London Bridge. Dominic Lipinski/PA Images via Getty Images