It has been claimed that members of a suspected British Isis cell arrested last week may be linked to those who plotted the Berlin Christmas market truck attack.
Four men from Derby, aged 22, 27, 35 and 36, a 27-year-old man from Burton upon Trent and a 32-year-old woman from London were arrested on 12 December on suspicion of preparing an act of terrorism. Sources said the group may have wanted to bomb a shopping centre in the UK in the run-up to Christmas.
The Sun reported that the suspects might have been in contact with Isis leaders working in Syria. A US security source told the paper there was evidence UK suspects were being "directed by an IS external operations group based out of Aleppo in Syria".
There was also evidence that a UK group was looking at launching a "relatively small" attack in conjunction with other Isis cells in Europe to test security responses, the paper reported.
Meanwhile, Olivier Guitta, the managing director of security consultancy GlobalStrat, told the Sun Online that the decision by the Berlin truck killer not to die at the scene of the attack on Monday (19 December) hinted that he may be planning another atrocity.
"In most recent cases of successful Islamic State attacks, the terrorists planned to kill themselves or be killed by counter-terrorism forces – i.e, become a martyr," he said.
Isis said one of its "soldiers" carried out the attack in Berlin which killed 12 people, although German authorities have not verified the claim. The only suspect, identified as Pakistani national Nayed B, was released due to insufficient evidence.
A police source told Die Welt newspaper: "We have the wrong man. This means the situation is different. The real culprit is still armed and can commit further atrocities."
Police in London have stepped up security and brought forward plans to close roads around Buckingham Palace during the Changing of the Guard ceremony, the BBC reported.
In the aftermath of the horror, the German chancellor, Angela Merkel, has been criticised over her decision to welcome refugees. The leader of the right-wing Alternative for Germany party (AFD), Frauke Petry, warned that "radical Islamist terrorism has struck in the heart of Germany".
Horst Seehofer, leader of the CSU which is part of Merkel's CDU/CSU bloc in parliament, said the attack meant that Germany needs to change its immigration policies.