LONDON » Britain is bracing for clashes with right-wing activists and possible copycat terror attacks by Islamic extremists after the savage slaying of a young soldier, whose grieving family spoke today of their loss.

London police said more than 1,000 officers will be sent to potential trouble spots with armed response units. Most British police officers don’t carry weapons.

Wednesday’s attack was captured on video by passersby and made for gruesome viewing — one man is seen with his hands stained red with blood and holding two butcher’s knives as he angrily complained about the British government and troops in foreign lands. A lifeless body is seen on the street behind him.

Terror analysts say the attackers wanted the publicity to inspire copycat attacks, and that they are already seeing an increase in chatter on extremist sites calling for such attacks.

"We can see the tempo being raised," said Maajid Nawaz, a former jihadist who is now with the London-based anti-extremist Quilliam Foundation.

"One of the reasons why these guys acted in this theatrical way was because of the propaganda effect so others would be inspired to do the same thing. The nature of these attacks are that they are so easy to do, and we have definitely seen an increase in chatter calling for such things since the attack."

A British government official who spoke on condition of anonymity because he wasn’t authorized to speak about the ongoing investigation, confirmed the increase in chatter since Wednesday’s attack but said no specific or credible plots had been detected at this point.

Britain’s terror threat level has remained unchanged at "substantial" — the middle of five possible rankings — since the slaying of 25-year-old Drummer Lee Rigby.

Police said today that an autopsy on Rigby’s remains had been conducted but that the cause of death "has not been confirmed." Police said an inquest will be held.

His anguished widow, Rebecca Rigby, spoke of her loss today at a news conference at his unit’s headquarters.

"I love Lee and always will," she said, sobbing. "I am proud to be his wife and he was due to come up this weekend so we could continue our future together as a family."

She said she never expected her husband to be in danger while in Britain: "You don’t expect it to happen when he’s in the UK. You think they’re safe." His stepfather, Ian Rigby, read a statement on the family’s behalf, including the final text the soldier had sent to his mother, who was too upset to speak.

"The last text he sent to his mum read, ‘Goodnight mum, I hope you had a fantastic day today because you are the most fantastic and one in a million mum that anyone could ever wish for. Thank you for supporting me all these years, you’re not just my mum, you’re my best friend. So goodnight, love you loads," Ian Rigby said.

Right-wing extremists, meanwhile, said they would be holding demonstrations over the coming weeks. Several dozen gathered the night of the slaying to protest.

There were some signs of a backlash against Muslims, including two incidents late Thursday night. In Lincolnshire, police said 11 teenagers were arrested after they attacked a local mosque following a party. In the other attack, a burning bottle was thrown at a mosque in Bletchley while people inside were praying, Thames Valley Police said. There was minor damage to the mosque, but no injuries were reported.

Police today released without charge a 29-year-old woman who had been arrested as part of the murder inquiry, and also released a 31-year-old woman who had been arrested late Thursday. A 29-year-old man arrested Thursday remains in custody.

The two main suspects, who were shot after rushing police who arrived on the murder scene, are receiving hospital treatment for their wounds.

Britain’s domestic spy agency of MI5 has long warned of the difficulties in predicting self-starter attacks, or attacks that are inspired — not necessarily organized — by larger groups.

With the weakening of al-Qaida’s leadership structure in Afghanistan and Pakistan, there has been an increase in lone-wolf attacks, which are low-tech and relatively easy to pull off.

Both suspects in the soldier’s killing were on the agency’s radar for as long as six years. Video footage showed one of the men at a 2007 rally with Anjem Choudary, the former leader of the banned extremist group al-Muhajiroun.

But the men weren’t necessarily the focus of any specific investigation, according to the British official who spoke on condition of anonymity. There has to be compelling intelligence to suggest a real threat before suspects are put under surveillance.

"It is a democratic right to protest in this country," the British official said. "Not everyone who shows up at a demonstration, even though they may say or believe in things that we don’t, will turn to violence."