Labour leader Ed Miliband said the killing of a man in Woolwich is a "truly appalling murder".
Mr Miliband, cutting short a Germany visit to return to the UK, said his party offered the Government " complete support".
He said: "This is a truly appalling murder which will shock the entire country.
“All of my thoughts are with the family and friends of the victim.
“The British people will be horrified by what has happened in Woolwich. Theywill be united in believing that this terror on our streets cannot be allowedto stand.
“The Labour Party will offer the Government our complete support in establishing the facts of what happened and ensuring that those responsible face the full force of British justice."
A 13-year-old girl is among five people arrested in connection with a murder inquiry after a man's body was found in a country lane in South Yorkshire.
A 47-year-old woman and three men, aged 21, 27 and 31, have also been arrested by detectives.
Nottinghamshire Police today launched a murder investigation after the man was found in countryside near Doncaster, by the border with Yorkshire, on Saturday 2 February.
The results of a post-mortem examination have so far proven inconclusive.
A woman has been charged with the murder of a two-year-old boy.
Angela Vane, 40, from Champernowne, Modbury, Devon, will appear before Torquay Magistrates' Court tomorrow charged over the toddler's death, Devon and Cornwall Police said.
Officers were called to a home in Modbury yesterday morning after the boy's body was discovered by a member of the public.
His identity has not been released.
Police have carried out door-to-door inquiries and initial forensic work, although it is believed a post-mortem examination has yet to be carried out.
The post-mortem examination of a two-year-old boy is expected to be carried out in the coming days by a Home Office pathologist or specialist paediatric pathologist. Detectives are continuing to piece together information and urged members of the public with any information to get in touch.
At around 8.20am [on Saturday], following a report to police, officers attended an address in Champernowne, Modbury, where they found the body of a two-year-old boy.A 40-year-old local woman has been arrested on suspicion of murder and is currently in custody at Charles Cross police station, Plymouth.
Detectives have launched a murder investigation following the death of a two-year-old boy. Officers were called to a home in Modbury, Devon, yesterday morning after the little boy's body was discovered by a member of the public.
Police confirmed they have arrested a woman and she is being questioned by officers on suspicion of murder. As well as carrying out door-to-door enquiries, police have also begun initial forensic work - although it is believed a post-mortem examination has yet to be carried out.
Detectives investigating the murder of Sheffield church organist Alan Greaves on Christmas Eve have released CCTV footage of two men they want to question about the killing. The new images were released at a press conference at South Yorkshire Police's training centre in Wath-upon-Dearne.
Norwegian mass murderer Anders Behring Breivik has released a 27-page letter bemoaning his conditions in prison.
The 33-year-old, who murdered 77 people in 2011, is currently serving a 21-year sentence.
In the letter he bemoaned the "800" strip searches he has had and the fact that he does not enjoy 'enough' social interaction.
According to the New York Times, Breivik is also not satisfied with his three-suite cell - which is fitted with a television and exercise equipment.
Four men have been arrested on suspicion of attempted murder after a man was run over following an argument at a pub.
A 24-year-old was hit by a Volkswagen Golf R32 as he was walking near to the Esso Garage in Ascot, Berkshire, in the early hours of this morning.
He was rushed to hospital and is in a critical condition.
Four men are in police custody.
"Although we are in the early stages of the investigation, we believe that the injured man was possibly involved in a previous altercation at the Club One pub with a group of other men. It is vital that anyone who was in the area at the time and saw the collision, or the man in the club prior to this and has information to help us with our investigation, comes forward and speaks to the police."
The High Street in Ascot was closed following the incident at 3.20am as the police carried out their investigation.
The road is expected to be closed for several hours.
For more information read ITV News Meridian.
A 47-year-old man died in what police described as a vicious attack.
The victim, who was in a critical condition in hospital, died from his injuries.
Police arrested a 30-year-old man in connection with the serious assault, following the attack in the Dromore Street area of Ballynahinch.
Detectives in Downpatrick are quizzing him about the attack which was reported at around 12.45am.
A 16-year-old boy has been arrested on suspicion of murdering a woman, Dorset Police said.
The teenager was held after officers attended an address in Benville Road, Weymouth, Dorset, after reports that a woman had been injured.
When police arrived at the property at 1.06pm they discovered the woman's body.
Police said the woman's relatives have not yet been informed.