Weak border controls and urbanisation could have allowed the Ebola outbreak in west Africa to become so deadly, new analysis suggests.

Researchers claim the relatively free movement of people between Liberia, Sierra Leone and Guinea potentially contributed to the virus spreading internationally.

More than 11,000 people died as the disease took hold across the African nations between 2013, when the outbreak was thought to have begun in Guinea, and 2016, with a handful of cases treated in the UK.

A study, published in the Nature journal, found towns and cities located close to one another also had a bearing on the outbreak becoming so widespread, while heavily built-up areas might have allowed cases to multiply.

Other neighbouring countries might have escaped being seriously blighted by the virus due to their tighter borders, it added.

The paper, which is co-authored by scientists from the University of Edinburgh, the US and Belgium, said: "Porous borders between Liberia, Sierra Leone and Guinea may have allowed the unimpeded (Ebola virus) spread during the 2013-2016 epidemic."

But of the eventual lockdown of the three affected countries in 2014, it said: "It is difficult to ascertain whether the border closures themselves were responsible for the apparent reduction in cross-border transmissions, as opposed to concomitant control efforts or public information campaigns.

"However, even if border closures reduced international traffic, particularly over longer distances and between larger population centres, by the time that Sierra Leone and Liberia had closed their borders, the epidemic had become firmly established in both countries."

The findings come as British Ebola survivor Pauline Cafferkey said she was planning to return to Sierra Leone for the first time since she became infected by the virus.