The first person to be diagnosed with Ebola within the US has died, Texas hospital officials have said.
Mr Duncan, shown here at a 2011 wedding in Ghana
Thomas Eric Duncan, 42, who caught the virus in his native Liberia, was being treated with an experimental drug in isolation in a Dallas hospital.
Earlier the US announced new screening measures at entry points to check travellers for symptoms of the virus.
It has killed 3,865 people, mostly in Liberia, Sierra Leone and Guinea, in the worst Ebola outbreak yet.
"It is with profound sadness and heartfelt disappointment that we must inform you of the death of Thomas Eric Duncan this morning at 7:51 am," a spokesman for Texas Health Presbyterian Hospital in Dallas said in a statement.
"Our thoughts today are with his family," said US President Barack Obama, who said his death showed "we don't have a lot of margin for error. If we don't follow protocols and procedures that are put in place, then we're putting folks in our communities at risk".
The news came shortly after US Secretary of State John Kerry urged all nations to boost their response to combat the virus.
"More countries can and must step up," he said in a joint press conference with his British counterpart Philip Hammond.
The US has pledged as many as 4,000 troops to the region, while the UK is sending 750 military personnel to Sierra Leone.
Duncan, who worked as a driver for a courier company, tested positive in Dallas on 30 September, 10 days after arriving on a flight from Monrovia via Brussels.
He become ill a few days after arriving in the US. Even after going to hospital and telling medical staff he had been in Liberia, he was sent home with antibiotics.
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