UK police are stepping up armed patrols on the transport network and in other crowded places, as they warn of an increased terror risk over the festive period.
Senior officers from Counter Terror Policing and the British Transport Police have issued a joint call for vigilance following the recent attacks targeting the Jewish community in Manchester and Australia.
They warn that mass gatherings over the Christmas and New Year period "remain an attractive target for terrorists".
The call for vigilance follows news of foiled terror plots targeting a Christmas market in Germany and New Year celebrations in Los Angeles.
The US Attorney General Pam Bondi said authorities had prevented "far-left" extremists from executing "a massive and horrific terror plot".
The FBI confirmed that four alleged members of the Turtle Island Liberation Front, an offshoot of a pro-Palestinian anti-government group, were arrested on suspicion of planning a series of coordinated bomb attacks in at least five locations across southern California.
Officials said that members of the group were detained after traveling to a desert location near Los Angeles to test improvised explosive devices.
On Monday, German law enforcement officials confirmed they had foiled a plot to attack a Christmas market in southern Bavaria.
Police officers in Oxford Street during the festive period
|PA
An Egyptian imam, three Moroccans and a Syrian were arrested over the plot to allegedly kill as many people as possible in a vehicle-borne attack.
While GB News understands there is no specific intelligence of any planned attack in the UK, the period leading up to Christmas and New Year is always seen as particularly high risk, as many more members of the public gather in significant numbers at high profile events.
In a statement, Counter Terrorism Policing said: "Sadly, we know that the things which bring us together remain an attractive target for terrorists".
The Senior National Coordinator for Protect and Prepare, Deputy Assistant Commissioner Jon Savell added: "I know that this year, we find ourselves entering the festive season with the recent terrible attack in Manchester fresh in our minds, along with the awful atrocity in Australia just days ago.
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15 people were killed in the Bondi Beach attack | REUTERS"These awful acts remind us that the vigilance of our communities has never been more important. Staying safe is a shared responsibility, and this winter, we hope that it's a mantle taken up by the many.
"Every single report we receive from the public is important, you won't be wasting our time if you call us or report something online. Each report you make could make a different to investigations, or even create the opportunity for arrests or other action."
Last year, one in five of the reports to the Anti-Terrorism Hotline and the online equivalent were passed on to specialist officers for further investigation.
Across the UK's transport network, authorities say there will be a visible increase in police patrols in the days ahead.
The British Transport Police is stepping up its patrols
| PABritish Transport Police Chief Constable Lucy D'Orsi said: "The railway network is always busy throughout the festive period, packed with shoppers, partygoers, tourists and people visiting family and friends.
"You will notice more BTP officers, including armed police and search dog teams, on trains and at stations, and there will also be officers there who you won't be able to see.
"They are there to keep you safe, but we need your help too. If something doesn't feel right, trust your instincts and tell us."
In October, the Director General of MI5, Sir Ken McCallum warned the service was "dealing with near-record volumes of terror investigations".
The spy chief said that al-Qaeda and the Islamic State terror groups were "once again becoming more ambitious" and "taking advantage of instability overseas to gain firmer footholds".
The terror threat level in the UK is currently at SUBSTANTIAL, which means a terrorist attack is likely.