Islamist militants have released a video in which they appear to call for terrorist attacks on some of the busiest shopping areas in the UK and US.

In the footage, fighters from the al-Shabaab group specifically mention Oxford Street in London, and give GPS coordinates for the Westfield shopping centres in Stratford and Shepherd's Bush.

US authorities have said they are taking the threats seriously, while the Metropolitan Police said its Counter Terrorism Command is aware of the video and is assessing the content.

The Somali-based militants have previously claimed responsibility for the 2013 attack on an upmarket shopping mall in Kenya, which left 67 people dead.

Several US shopping malls were also threatened in the video, which was released on Saturday.

One of them, the Mall of America in Minnesota, has already increased security amid fears that radicalised Muslims could orchestrate an attack. The state is home to a sizeable Somali population.

Jeh Johnson, the chief of homeland security in the US, said: "Anytime a terrorist organization calls for an attack on a specific place, we've got to take that seriously."

"I would say that if anyone is planning to go to the Mall of America today, they've got to be particularly careful."