The terror threat level has been reduced from "critical" to "severe" after two men were arrested in conjunction with the Parsons Green Tube terror attack, Amber Rudd has announced.

The Home Secretary said police have made "good progress" with their investigation.

"Severe" means a terrorist attack is thought to be highly likely, whereas "critical" suggests it is imminent.

Soldiers who had been drafted in to guard public sites in order to free up police resources will "return to their original positions" over the next few days, Ms Rudd said.

Terror attack at Parson's Green – in pictures Show all 23 1 /23 Terror attack at Parson's Green – in pictures Terror attack at Parson's Green – in pictures Parsons Green explosion A bucket with flames and wires coming out of it was photographed in the carriage after the explosion – apparently the source of the blast AFP Terror attack at Parson's Green – in pictures Parsons Green explosion An explosion on a packed Tube train has injured a number of people in west London AFP/Getty Terror attack at Parson's Green – in pictures Parsons Green explosion The blast triggered a stampede as commuters panicked AFP/Getty Terror attack at Parson's Green – in pictures Parsons Green explosion Click through for more pictures from the scene Reuters Terror attack at Parson's Green – in pictures Parsons Green explosioN A police officer and a sniffer dog stand in the street near Parsons Green tube station in London, Britain September 15, 2017. REUTERS/Kevin Coombs Reuters Terror attack at Parson's Green – in pictures Parsons Green explosion Handout photo issued by James Treen of emergency services attending an incident at Parsons Green station in west London amid reports of an explosion. PRESS ASSOCIATION Photo. Issue date: Friday September 15, 2017. See PA story TRANSPORT Explosion. Photo credit should read: James Treen/PA Wire NOTE TO EDITORS: This handout photo may only be used in for editorial reporting purposes for the contemporaneous illustration of events, things or the people in the image or facts mentioned in the caption. Reuse of the picture may require further permission from the copyright holder. PA Terror attack at Parson's Green – in pictures Parsons Green explosion Police vehicles line the street near Parsons Green tube station in London, Britain September 15, 2017. REUTERS/Kevin Coombs Reuters Terror attack at Parson's Green – in pictures Parsons Green explosion A police officer stands outside Parsons Green tube station in London, Britain September 15, 2017. REUTERS/Kevin Coombs Reuters Terror attack at Parson's Green – in pictures Parsons Green explosion Armed British police officers stand on duty outside Parsons Green underground tube station in west London on September 15, 2017, following an incident on an underground tube carriage at the station. Police and ambulance services said they were responding to an "incident" at Parsons Green underground station in west London on Friday, following media reports of an explosion. A Metro.co.uk reporter at the scene was quoted by the paper as saying that a white container exploded on the train and passengers had suffered facial burns. / AFP PHOTO / Daniel LEAL-OLIVAS / ===RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT "AFP PHOTO / HO / @RRIGS - NO MARKETING NO ADVERTISING CAMPAIGNS NO ARCHIVES - DISTRIBUTED AS A SERVICE TO CLIENTS FROM FROM ALTERNATIVE SOURCES, THEREFORE AFP IS NOT RESPONSIBLE FOR ANY DIGITAL ALTERATIONS TO THE PICTURE'S EDITORIAL CONTENT, DATE AND LOCATION WHICH CANNOT BE INDEPENDENTLY VERIFIED == / DANIEL LEAL-OLIVAS/AFP/Getty Images AFP/Getty Terror attack at Parson's Green – in pictures Parsons Green explosion Emergency services attend the scene following a blast on an underground train at Parsons Green tube station in West London, Britain September 15, 2017, in this image taken from social media. TWITTER / @ASolopovas/via REUTERS THIS IMAGE HAS BEEN SUPPLIED BY A THIRD PARTY. NO RESALES. NO ARCHIVES. MANDATORY CREDIT Reuters Terror attack at Parson's Green – in pictures Parsons Green explosion Armed British police officers stand on duty outside Parsons Green underground tube station in west London on September 15, 2017, following an incident on an underground tube carriage at the station. Police and ambulance services said they were responding to an "incident" at Parsons Green underground station in west London on Friday, following media reports of an explosion. A Metro.co.uk reporter at the scene was quoted by the paper as saying that a white container exploded on the train and passengers had suffered facial burns. / AFP PHOTO / Daniel LEAL-OLIVAS / ===RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT "AFP PHOTO / HO / @RRIGS - NO MARKETING NO ADVERTISING CAMPAIGNS NO ARCHIVES - DISTRIBUTED AS A SERVICE TO CLIENTS FROM FROM ALTERNATIVE SOURCES, THEREFORE AFP IS NOT RESPONSIBLE FOR ANY DIGITAL ALTERATIONS TO THE PICTURE'S EDITORIAL CONTENT, DATE AND LOCATION WHICH CANNOT BE INDEPENDENTLY VERIFIED == / DANIEL LEAL-OLIVAS/AFP/Getty Images AFP/Getty Terror attack at Parson's Green – in pictures Parsons Green explosion Armed British police officers stand on duty outside Parsons Green underground tube station in west London on September 15, 2017, following an incident on an underground tube carriage at the station. Police and ambulance services said they were responding to an "incident" at Parsons Green underground station in west London on Friday, following media reports of an explosion. A Metro.co.uk reporter at the scene was quoted by the paper as saying that a white container exploded on the train and passengers had suffered facial burns. / AFP PHOTO / Daniel LEAL-OLIVAS / ===RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT "AFP PHOTO / HO / @RRIGS - NO MARKETING NO ADVERTISING CAMPAIGNS NO ARCHIVES - DISTRIBUTED AS A SERVICE TO CLIENTS FROM FROM ALTERNATIVE SOURCES, THEREFORE AFP IS NOT RESPONSIBLE FOR ANY DIGITAL ALTERATIONS TO THE PICTURE'S EDITORIAL CONTENT, DATE AND LOCATION WHICH CANNOT BE INDEPENDENTLY VERIFIED == / DANIEL LEAL-OLIVAS/AFP/Getty Images AFP/Getty Terror attack at Parson's Green – in pictures Parsons Green explosion Armed policemen stand by cordon near Parsons Green tube station in London, Britain September 15, 2017. REUTERS/Hannah McKay Reuters Terror attack at Parson's Green – in pictures Parsons Green explosion A woman reacts outside Parsons Green tube station in London, Britain September 15, 2017. REUTERS/Kevin Coombs Reuters Terror attack at Parson's Green – in pictures LONDON, ENGLAND - SEPTEMBER 15: Emergency services outside of Parsons Green Underground Station on September 15, 2017 in London, England. Several people have been injured after an explosion on a tube train in south-west London. The Police are treating the incident as terrorism. (Photo by Jack Taylor/Getty Images) Getty Terror attack at Parson's Green – in pictures LONDON, ENGLAND - SEPTEMBER 15: A fireman walks past the police cordon at Parsons Green Underground Station on September 15, 2017 in London, England. Several people have been injured after an explosion on a tube train in south-west London. The Police are treating the incident as terrorism. (Photo by Jack Taylor/Getty Images) Getty Terror attack at Parson's Green – in pictures LONDON, ENGLAND - SEPTEMBER 15: A tube train is seen stopped at Parsons Green Underground Station on September 15, 2017 in London, England. Several people have been injured after an explosion on a tube train in south-west London. The Police are treating the incident as terrorism. (Photo by Chris J Ratcliffe/Getty Images) Getty Terror attack at Parson's Green – in pictures LONDON, ENGLAND - SEPTEMBER 15: Police officers stand by a cordon at Parsons Green Underground Station on September 15, 2017 in London, England. Several people have been injured after an explosion on a tube train in south-west London. The Police are treating the incident as terrorism. (Photo by Jack Taylor/Getty Images) Getty Terror attack at Parson's Green – in pictures Police forensics officers works alongside an underground tube train at a platform at Parsons Green underground tube station in west London on September 15, 2017, following an incident on an underground tube carriage at the station. Police and ambulance services said they were responding to an "incident" at Parsons Green underground station in west London on Friday, following media reports of an explosion. "We are aware of an incident at Parsons Green tube station. Officers are in attendance," London's Metropolitan Police said on Twitter. / AFP PHOTO / Daniel LEAL-OLIVAS / (Photo credit should read DANIEL LEAL-OLIVAS/AFP/Getty Images) AFP/Getty Terror attack at Parson's Green – in pictures LONDON, ENGLAND - SEPTEMBER 15: Emergency serivces attend to the scene near Parsons Green Underground Station on September 15, 2017 in London, England. Several people have been injured after an explosion on a tube train in south-west London. The Police are treating the incident as terrorism. (Photo by Jack Taylor/Getty Images) Getty Terror attack at Parson's Green – in pictures Members of the emergency services work outside Parsons Green underground tube station in west London on September 15, 2017, following an incident on an underground tube carriage at the station. British police are treating an incident on a London Underground train on Friday as an act of terrorism, saying "a number of people" had been injured. "Terrorist incident declared at Parsons Green Underground Station," police said in a statement. / AFP PHOTO / Daniel LEAL-OLIVAS (Photo credit should read DANIEL LEAL-OLIVAS/AFP/Getty Images) AFP/Getty Terror attack at Parson's Green – in pictures Armed British police officers walk through the carriage of a London underground tube carriage at Parsons Green underground tube station in west London on September 15, 2017, following an incident on an underground tube carriage at the station. Police and ambulance services said they were responding to an "incident" at Parsons Green underground station in west London on Friday, following media reports of an explosion. A Metro.co.uk reporter at the scene was quoted by the paper as saying that a white container exploded on the train and passengers had suffered facial burns. / AFP PHOTO / Daniel LEAL-OLIVAS (Photo credit should read DANIEL LEAL-OLIVAS/AFP/Getty Images) AFP/Getty Terror attack at Parson's Green – in pictures Members of the emergency services and armed police officers work alongside an underground tube train at a platform at Parsons Green underground tube station in west London on September 15, 2017, following an incident on an underground tube carriage at the station. Police and ambulance services said they were responding to an "incident" at Parsons Green underground station in west London on Friday, following media reports of an explosion. "We are aware of an incident at Parsons Green tube station. Officers are in attendance," London's Metropolitan Police said on Twitter. / AFP PHOTO / Daniel LEAL-OLIVAS (Photo credit should read DANIEL LEAL-OLIVAS/AFP/Getty Images) AFP/Getty

The Home Secretary said the Joint Terrorism Analysis Centre (JTAC), which determines the terror threat level, had decided that "sufficient progress" has been made in the Parsons Green investigation to lower the threat.

Isis has claimed responsibility for the attack, which left 30 people injured when a bomb partially exploded on a District Line train on Friday morning. However, the Metropolitan Police said it was "routine" for the group to claim it was behind attacks in which it has actually had little direct involvement.

Responding to reported Isis claims that its followers have manufactured further explosive devices in London, Ms Rudd said: "They will always make claims that suit their intentions, but actually there is no evidence of that."

Speaking shortly after the Home Secretary, the Met Police's Assistant Commissioner, Mark Rowley, who is also National Lead for Counter Terrorism Policing, provided an update on the Parsons Green investigation.

He said: "The high pace and rapid progress of this investigation is continuing. There was another arrest overnight and two men are in custody. There are now two searches continuing at addresses in Hounslow and Surrey and we are getting a greater understanding of the preparation of the device.

“There is still much more to do but this greater clarity and this progress has led JTAC – the independent body that assess threat – to come to the judgement that an attack is no longer imminent. And you will have heard consequently the Home Secretary’s announcement that the threat level has reduced from Critical to Severe which of course means that an attack is highly likely.

“The military support we have had in place under Operation Temperer will start to phase out as we move through the coming week. There are detailed and well-rehearsed plans in place to ensure a smooth transition from Operation Temperer, and military personnel will remain at readiness to deploy in support of the police should future security situations require.