The Bishop of Woolwich has said he is "deeply saddened and distressed" to hear of a fatal machete attack on a man in south-east London.
There are unconfirmed reports that the man killed was a soldier at the Woolwich barracks.
Two suspects were shot by police at the scene. Prime Minister David Cameron said there were "strong indications that this is a terrorist incident".
"We have had these sorts of attacks before in our country and we never buckle in the face of them," he said.
The Prime Minister has asked Home Secretary Theresa May to convene a meeting of the government's emergency response committee Cobra.
A witness, named only as James, told LCB radio that two men attacked a young man wearing a T-shirt of the Help for Heroes charity.
James described the attack as "horrendous", saying the two attackers were "crazed".
"They were just animals. They dragged him from the pavement and dumped his body in the middle of the road and left his body there," he told the station.
Disturbing footage has been broadcast by ITV on its website showing a man with bloodied hands holding a knife as he speaks to the camera, saying: "...we swear by almighty Allah, that we will never stop fighting you. Until you leave us alone, your people will never be safe."
He continues: "...the only reason we have done this is because Muslims are dying by British soldiers every day. This British soldier is an eye for eye, a tooth for a tooth."
St Mary Magdalene Church, in Woolwich's Greenlaw Street, has opened its doors to members of the public wanting to pray and reflect.
The Bishop of Woolwich, Dr Michael Ipgrave said the incident was "tragic".
He said: "I am deeply saddened and distressed to hear of the incident in John Wilson Street this afternoon. My thoughts and prayers are with the victim, his family and the local community."
Christians also took to Twitter after the attack:
God and Politics UK @GodandPolitics Terrible stuff in #woolwich. praying for the family and that words of peace would be louder than those of hatred right now.
Alastair Cutting @AlCutting Prayers in Woolwich this evening for those affected by this afternoons attack. Deep peace of the Prince of Peace
Sr CatherineWybourne @Digitalnun We pray for the man who has been killed and those injured in Woolwich, and for the safety of our security forces.
Andy Campbell @roguepioneer #pubnprayers in 30 - as ever, there will be some prayer for victims of violence worldwide...
Peter Ould ☩ @PeterOuld Praying for our armed forces tonight and especially my local regiment the Princess of Wales Royal Regiment based in Canterbury
