More than 1,000 supporters of Britain's far-right English Defence League group gathered in London on Monday for a protest over the death of a British soldier.
At the protest, outside of Downing Street, EDL leaders blamed Islam for the death of Drummer Lee Rigby, who was killed in Woolwich last week, The Guardian reported.
"I am here to show that we stand together against the killers of Lee Rigby. It seems that there is one law today for Muslims and one for everyone else," said Ben Roberts, a former soldier who spoke at the protest.
The EDL demonstration sparked a counter-protest organized by anti-fascist groups. Both protests were peaceful until several glass bottles were thrown between the crowds.
Police dispersed the groups and made three arrests, police said.
Meanwhile, the counter-terrorism command of London's Metropolitan Police Service arrested an unidentified 22-year-old man in inner London's Highbury district Sunday on suspicion of conspiracy to commit murder in the gruesome stabbing death of 25-year-old Rigby, police said.
"The guy was on a push bike when the police came out of nowhere and wrestled him to the ground," a witness told The Guardian.
No shots were fired, police said of the suspect held at a south London police station Monday.
Three other men in their 20s, arrested on the same charges Saturday, were released on bail pending further inquiries, police said Sunday night.
The two primary suspects in Rigby's murder -- Michael Adebolajo, 28, and Michael Adebowale, 22 -- remained in custody in separate London hospitals after being shot by police Wednesday.
They "will be formally interviewed when it is possible to do so," police said.
Rigby, of the 2nd Battalion, the Royal Regiment of Fusiliers, was run over and attacked with butcher knives and meat cleavers Wednesday as he walked back to his barracks in south London's Woolwich district, witnesses said.
He'd served in Afghanistan, Cyprus and Germany and was the father of a 2-year-old boy.
A 29-year-old man arrested Thursday on suspicion conspiring in the murder, and believed to have family links to Adebolajo, was also released on bail, police said, while two women arrested with him and held on suspicion of conspiring in the murder were released without being charged.
Kenyan authorities said, meanwhile, they arrested Adebolajo in 2010 with a group of suspected terrorists and returned him to British intelligence officers, who Kenya said failed to take their concerns seriously.
Britain's Home Office, responsible for immigration, security and law enforcement, confirmed the arrest and deportation Sunday.
It declined further comment -- nor would it comment on reports Adebolajo had tried to enter Somalia to join militants.
British officials face growing questions over their past interactions with Adebolajo and Adebowale.
Cameron has promised a full investigation by Parliament's Intelligence and Security Committee amid outrage both main suspects were known to the MI5 domestic security service and police but neither was considered a major security risk.
He also announced a new task force late Saturday on "tackling" extremism and radicalization in Britain.
But he was quickly criticized by opposition lawmakers for then leaving the country for a weeklong vacation at a private villa with his family on the Spanish Mediterranean island of Ibiza.
British newspapers showed a photo of Cameron and his wife Samantha relaxing in an outdoor cafe by a white-sands beach, while opposition politicians expressed outrage he left the country after the worst terrorist atrocity on British soil since 52 people were killed in four coordinated suicide bombings targeting London's transit system July 7, 2005.
Downing Street said Cameron "remains in charge," having taken a small team of key staff with him so he can be kept informed of the murder investigation.
But John Mann, a British Labor member of Parliament, told the Telegraph: "People expect him to be at his desk leading from the front. It is inappropriate that he is away. It suggests that he thinks he can run the country from a beach in Spain.