Ten people have been arrested on suspicion of murder after a police officer was killed while responding to a reported burglary in Berkshire.
PC Andrew Harper, from the Roads Policing Proactive Unit based at Abingdon police station, was on duty when he died.
Thames Valley Police said a 13-year-old boy was among those being held in custody at different police stations across the region.
The force said PC Harper died following a “serious incident” at 11.30pm on Thursday near the A4, Bath Road, between Reading and Newbury.
It occurred near the village of Sulhamstead and the road remains closed.
Images from the scene showed a police cordon in place with forensic teams at work.
Andy Fiddler, from Thames Valley Police Federation, said the death of PC Harper was “totally devastating”.
He said: “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.”
One officer, who said she knew PC Harper, recalled knowing a “brilliant” and “top officer” who was part of a case involving the arrest of her ex-husband for domestic violence.
She said: “He was brilliant and gave me the courage to take steps to change my life. I can’t thank him enough. He was a top officer.”
Prime Minister Boris Johnson said he was “deeply shocked and appalled by the death of a brave officer on duty”.
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.”
Thursday’s incident is the latest in a string of recent violent incidents involving police officers.
It comes after PC Stuart Outten, 28, was attacked with a machete in London last week by a motor offences suspect, and just days after PC Gareth Phillips, 42, suffered “potentially life-changing” injuries after he was run over by a suspected car thief in Birmingham.
Earlier this month, Mr Johnson pledged to make the country’s policing a top priority, and promised to make way for 10,000 extra prison places and 20,000 more police officers.
Home Secretary Priti Patel said she would do “everything in my power” to support police officers and “crack down on cowardly criminals who commit appalling acts of violence”.
She said: “PC Harper died in the line of duty protecting the public and his incredible bravery and extraordinary sacrifice will not be forgotten.
“Our dedicated police officers go to work every day to serve their communities. They are courageous and professional people who confront danger on a daily basis. The risks they take to keep us all safe are enormous.”
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. (2/2)
— Boris Johnson (@BorisJohnson) August 16, 2019
Labour leader Jeremy Corbyn said he was “totally shocked”. He added: “Let’s just think for a moment of the horror of it, but also for the need for more police officers to be able to respond to disorder in our society, but also the problem of guns and the problem of violence that is growing.”
Shadow policing and crime minister Louise Haigh also tweeted about the “horrific news”, adding: “[Although] it won’t bring him back, I hope the culprit is swiftly brought to justice.”
Anthony Stansfeld, the police and crime commissioner for Thames Valley, said he was sending “deepest condolences” to the family and friends of PC Harper.
He added: “This is a tragic loss for the force and I know that Thames Valley Police are doing all they can to support those who have been affected.”
Other policing departments around the country have also tweeted their support for Thames Valley Police following the news of the death.
Derbyshire Roads Policing Unit said it was “every cop’s worst nightmare” to wake up to, while Lancashire Police said it “stands shoulder to shoulder” with its colleagues.
Police are appealing for any witnesses to come forward.
Any person with information relevant to the ongoing case can call 101 or leave details on the Thames Valley Police website.