The militant network behind last month's attacks in Paris had links to people in Britain, the Wall Street Journal has said in a report that British police described on Saturday as "speculative".
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Several people suspected of having connections to Abdelhamid Abaaoud, the Islamic State militant and alleged ringleader of the Nov. 13 attacks, are based in Britain, according to two unidentified Western officials the Journal cited late on Friday.
The officials told the Journal those people, including some of Moroccan heritage, were based in the Birmingham area in central England, about 120 miles (190 km) from London.
There has been no official suggestion in London of any direct links between the group that carried out the attack that killed 130 people and British militants. But jihadi groups are often loosely arranged and contacts, including the use of social media, are widespread.
West Midlands Police, based in Birmingham, said on Saturday that media reports regarding the Paris attackers and potential contact with people or places in the city were "speculative".
Assistant Chief Constable Marcus Beale said the force's counter-terrorism unit was "working hand-in-hand" with counter-terrorism colleagues in London, the national counter-terrorism network and security services to provide support to the French and Belgian investigations into the attacks.
Britain's Mirror newspaper reported that British police were investigating claims that a member of the gang that attacked Paris made several phone calls to Birmingham in the run-up to the atrocity.
"They were made shortly before the Paris attacks. British police are urgently investigating whether anyone in the UK was involved in those atrocities and also whether there is a linked terror cell based here," the Mirror cited a source as saying.
Britain suffered by far its worst militant Islamist attack in July, 2005, when 52 people were killed by suicide bombs on underground trains and a bus.
Britain is on its second-highest alert level of "severe", meaning a militant attack is considered highly likely. This is mainly due to the threat the authorities say is posed by Islamic State militants in Syria and Iraq and their encouragement of supporters to carry out attacks in their homelands.
Charles Farr, the director general of the Office for Security and Counter-Terrorism, said last month that up to 800 Britons had traveled to Iraq and Syria, some to join Islamic State. About 50 percent had returned home while about 70 were believed to have been killed, Farr said.
Britain says seven plots have been foiled in the last year, although not on the same scale as those carried out in Paris, and counter-terrorism officers make on average an arrest every day.