A UN employee infected with Ebola has died at a hospital in Germany.

The Ebola patient was being treated at a clinic for infectious diseases at St. Georg Hospital in Leipzig, Germany, 9 October 2014.

Doctors at the hospital in Leipzig said the man, 56, died despite receiving experimental drugs to treat the virus.

The outbreak has killed more than 4,000 people since March - mostly in Liberia, Sierra Leone, Guinea and Nigeria.

The World Health Organization described it as the "the most severe, acute health emergency seen in modern times". The US and UK are among countries to have introduced scanning at airports.

The man had been working as a UN medical official in Liberia - one of the worst affected countries - when he caught Ebola.

He arrived in Germany last Thursday for treatment and was put into a hermetically-sealed isolation ward which is accessed through airlock systems.

"Despite intensive medical measures and maximum efforts by the medical team, the 56-year-old UN employee succumbed to the serious infectious disease," a statement from St Georg hospital said.

He was the second member of the UN team in Liberia to die from the virus, the BBC's Jenny Hill in Berlin says.

The patient, who is yet to be identified, was reportedly Sudanese.

He was the third Ebola patient to be treated for the deadly virus in Germany after contracting the disease in the outbreak zone in West Africa.

One patient - a Ugandan doctor infected in Sierra Leone - is still receiving treatment in a hospital in Frankfurt, while a Senegalese aid worker was released from a hospital in Hamburg after five weeks of treatment.

Health workers are among those most at risk of catching the disease, with more than 90 killed by the virus in Liberia alone.

Many nurses and medical assistants there have ignored calls to strike over pay and working conditions.

The World Health Organisation (WHO) has warned the epidemic threatens the "very survival" of societies and could lead to failed states.

The UK has announced screening for passengers arriving at London's Heathrow airport from countries at risk.

People arriving from Liberia, Sierra Leone and Guinea will be questioned and may have their temperatures taken.

The US is already screening passengers at five of its major airports.