British officials did not identify him by name, but the French president, Francois Hollande, referred to the victim as "a soldier" in expressing France's sympathy to the visiting British prime minister, David Cameron, who was in Paris when the attack took place.
The two suspects were shot and wounded by armed police, officials said, and were in the hospital under police guard. One suspect was described as being in serious condition. One of the men shouted "Allahu akbar," or "God is great," as the attack proceeded, government officials said.
Cameron, who interrupted a European tour to return to London on Wednesday night, said at a news conference at the Elysee Palace in Paris that the killing was "an appalling murder" and "absolutely sickening."
"There are strong indications that it is a terrorist incident," Cameron said.
ITV News showed a video clip taken with a cellphone in which a man who appeared to be in his 20s or early 30s, holding a cleaver and knife with bloodied hands, offered what appeared to be a political message before the police arrived.
"I am sorry that women and children should have to see this," the man said. He then referred to what appeared to be a motive for the attack, saying that it had been carried out "because of what's going on in our own countries." That phrase has been used by militants to refer to conflicts in countries including Afghanistan, Iraq and Somalia.
The assault took place on a busy suburban street in Woolwich, the site of one of the main military barracks in London. A neighborhood primary school is nearby, and witnesses said that some of those who saw the attack were parents and children returning home from the school. (Read: Woman confronted attackers to deflect danger)
A small blue car involved in the ramming of the victim appeared to have collided with a telephone pole afterward. It was visible in photographs and television coverage of the scene, with extensive damage to its hood and front window.
Witnesses said they saw two men standing with blades over a man lying prone on the sidewalk, beside a wall. Shortly after the attack, these witnesses said, a man with a handgun leapt from an unmarked car and trained his gun on the assailants, shouting to passers-by to clear the area.
With Cameron in France, the home secretary, Theresa May, called an emergency meeting of the Cobra committee, a group of cabinet ministers and high-level security officials that oversees the operations of police and security agencies at times of high security alerts. Officials said that the group had ordered a tightening of security around all military barracks and other security facilities in Britain, including police stations. (Read: Protests over attack in London)
May described what had happened as a "sickening and barbaric attack."
"It has been confirmed to me that a man has been brutally murdered," she said after a meeting with the chief of Scotland Yard, Bernard Hogan-Howe, and Andrew Parker, the director general of MI5, the domestic security service. "Two other men were shot by armed police, and they are currently receiving treatment for their injuries."
In a Twitter post, the mayor of London, Boris Johnson, said the attack was a "sickening deluded and unforgivable act of violence." (See: Top websites, newspapers on London attack)