A 13-year-old boy is among ten people arrested on suspicion of murder after a Thames Valley police officer was killed near Sulhamstead, Berkshire.
PC Andrew Harper was responding to a reported burglary at around 11.30pm on Thursday when he was killed.
The suspects, all males aged between 13 and 30, are in police stations across the county.
It's been revealed that Pc Harper was married just four weeks ago.
Prime Minister Boris Johnson has said he is "shocked and appalled" by the death of "a brave officer".
He added: "My thoughts are with PC Harper's family, friends and colleagues at this terrible time.
"It is the most powerful reminder that police officers up and down the country put themselves at risk every single day to keep us safe.
"They have my absolute support."
A crime scene remains in place as police search the crossroads of Ufton Lane and Lambdens Hill, near to Sulhamstead.
The site of the killing is just a four minute drive away from the Sulhamstead police training centre.
Bath Road, A4 between Newbury and Reading has now reopened.
Home Secretary Priti Patel tweeted: "My thoughts are with the family of PC Andrew Harper who was killed in the line of duty last night."
Jeremy Corbyn said he was "totally shocked" by the death of PC Andrew Harper, and said it highlighted the need for more police officers on the streets.
He said: "I'm totally shocked at Andrew Harper's death, and my immediate thoughts are condolences to his family and to his colleagues who must be going through some awful moments at the present time.
"He was doing his duty apparently investigating a robbery of some sort, and was killed in the line of duty."
Deputy Chief Constable Jason Hogg said: “Our deepest thoughts at this time are of course with Andrew’s friends and family, who are being supported by specially trained family liaison officers.
“Our thoughts also extend to all of Andrew’s colleagues within Thames Valley Police.
“As a force we are devastated at the loss of our colleague and will all be supporting each other at this difficult time.”
Senior investigating officer Detective Chief Inspector Stuart Blaik, of the Thames Valley Police Major Crime Unit, said: “We have made a total of ten arrests in connection with this incident, and those arrested are currently in police custody.
"Those arrested are all male and aged between 13 and 30."
Andy Fiddler, from Thames Valley Police Federation, said: "This is totally devastating news. All our thoughts - and the thoughts of the entire police family across the UK - are with the family, friends and close colleagues of Pc Andrew Harper who died last night.
"Police officers go to work each and every day to do their duty. We are courageous, caring and compassionate. We confront danger on a daily basis. We know there is a risk when we put on the uniform but we do so as we are proud to protect the public.
"Sadly on very rare and horrendous occasions a colleague makes the ultimate sacrifice. We will ensure that heroism is never forgotten."
Any witnesses to the incident have been urged to come forward.
The incident in Berkshire comes after a police officer was slashed in the face after he stopped a van in Leyton.
PC Stuart Outten, 28, suffered severe head and hand injuries after he stopped a van suspected of having no insurance just after midnight on August 8.
Last Saturday, a suspected car thief was arrested after he ran over a police officer in Birmingham. A 29-year-old man remains in custody after being arrested on suspicion of the attempted murder of the constable who suffered head and pelvic injuries.