LONDON – Police, politicians and activists in Britain are warning of rising anti-Muslim sentiment following the slaughter of an off-duty British soldier in a London street, an apparent act of Islamic extremism that has horrified the nation.

Metropolitan Police investigating the killing of Lee Rigby, a 25-year-old soldier who was run over by attackers and then butchered with knives, arrested three more men in the murder investigation Saturday.

The latest arrests came as an estimated 1,500 members of an extremist right-wing group called the English Defense League marched in the northern English city of Newcastle, chanting Rigby’s name. In the southern English city of Portsmouth, police arrested two men for a racially motivated assault as hundreds of demonstrators gathered near one mosque, while several more people were detained for alleged racist offenses elsewhere.

The two men suspected of killing the soldier, Michael Adebolajo, 28, and Michael Adebowale, 22, remained under armed guard in separate London hospitals after police shot them at the scene. Police have not officially named the suspects because they have not been charged, but British officials speaking on condition of anonymity have confirmed their names.

Wednesday’s killing in southeast London’s Woolwich area shocked the nation partly because the horrific scenes were recorded on witnesses’ cellphones, and a video picked up by British media showed one of the two suspects, his hands bloodied, making political statements and warning of further violence as the soldier lay on the ground.

Police also are questioning a friend of Adebolajo who was arrested Friday night after he gave BBC Television an interview detailing why he thought Adebolajo may have become radicalized. Police said the friend, identified by the BBC as 31-year-old Abu Nusaybah, was wanted himself on suspicion of “the commission, preparation or instigation of acts of terrorism.”