A murder investigation has been launched after PC Andrew Harper was killed while performing his duties at a reported burglary in Berkshire.
Ten males between the ages of 13 and 30 have been arrested on suspicion of murder and are in police custody, according to Thames Valley Police.
The force said there was a "serious incident" at around 11.30pm on Thursday night near to the A4, between Reading and Newbury.
The statement added: "Tragically, Pc Andrew Harper from the Roads Policing Proactive Unit based at Abingdon Police Station, who was attending a reported burglary, was killed while performing his duties.
The Prime Minister called the incident a "powerful reminder" of the risks police officers take.
He wrote on Twitter: "I am deeply shocked and appalled by the death of a brave officer on duty in Thames Valley last night.
"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."
Deputy Chief Constable Jason Hogg said: "As a force we are devastated at the loss of our colleague and will all be supporting each other at this difficult time."
Andy Fiddler, from Thames Valley Police Federation, 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.”
Home Secretary Priti Patel has tweeted: "My thoughts are with the family of Pc Andrew Harper who was killed in the line of duty last night."