A Somali-based extremist group has named Westfield shopping centre in Stratford on a list of potential targets for terror attacks.

In a video released by al-Shabab, a man with a British accent and his face covered calls for "American or Jewish-owned" malls to be targted.

He mentioned both Westfield shopping centres in London and Oxford Street, as well as Minnesota's Mall of America and West Edmonton Mall in Canada, the BBC reports.

Map co-ordinates for the centres were also shown on screen.

US Homeland Security Secretary Jeh Johnson told CNN he took the threat seriously and warned people to be vigilant.