LONDON -- Prime Minister David Cameron vowed Thursday that his nation would not succumb to fear and promised a vigorous investigation into the brutal slaying of a British soldier by alleged Islamic extremists on a London street.

The killing appeared to be the first successfully executed terror attack since the coordinated transit system bombings in 2005.

Amid reports that at least one of the suspects had sought to travel to Somalia to support an al-Qaida affiliate, Cameron said there would be reviews of British security services' management of any information that had been received about either man in recent years. But he put the blame for the attack square on the "sickening individuals" who carried it out.

"The people who did this were trying to divide us," Cameron said. "They should know that something like this will only bring us together and make us stronger."

Britain's Defense Ministry identified the slain soldier as Army Drummer Lee Rigby, 25, of the 2nd Battalion of the Royal Regiment of Fusiliers. Rigby, who had a 2-year-old son named Jack, served with distinction in Afghanistan, Germany and Cyprus, authorities said.

The Times of London reported that the alleged assailants are British citizens of Nigerian background who had converted to a radical form of Islam.

Britain's Press Association said that although the men appeared to have links to Nigeria, they were not thought to have ties to terror groups based in that country.

British authorities have yet to publicly confirm the men's identities or backgrounds. But the BBC identified one of the suspects as Michael Adebolajo, 28, and described him as having been raised in a devout Christian family but converting to Islam after leaving college in 2001.

British officials arrested two other suspects Thursday -- a 29-year-old man and 29-year-old woman -- on suspicion of conspiracy to commit murder.

The two men suspected in Wednesday's attack allegedly struck their victim with a car and then hacked him to death in the southeast London neighborhood of Woolwich. The alleged assailants remained on the scene after the attack and were injured while being apprehended by police. They were being held at two separate London hospitals.

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