A British soldier was hacked to death by two men shouting Islamic slogans in a street in Woolwich, London on Wednesday (May 22), in what the government said appeared to be a terrorist attack.

"I'm afraid it's overwhelmingly likely now that this was indeed a terrorist incident of a kind that this city has seen before," London mayor Boris Johnson said in a statement.

"It was a sickening, barbaric, completely unforgivable crime."

Police said they later shot two suspects who were carrying weapons and took them into custody.

"We've launched an investigation led by the counter-terrorist command and we've made two arrests in relation to that awful crime," said metropolitan police commissioner Bernard Hogan-Howe.

Prime Minister David Cameron cut short a visit to France to return to London and chair an emergency national security meeting. He said there were strong indications that the killing was a terrorist incident.

As the government's emergency committee Cobra convened in central London to assess the implications of the incident, ITV News broadcast footage of one of the alleged attackers.

Brandishing a cleaver and a knife, and with the body of the victim lying yards away, the man said: "We swear by almighty Allah we will never stop fighting you. The only reason we have done this is because Muslims are dying every day. This British soldier is an eye for an eye, a tooth for a tooth."

Presented by Adam Justice