Describing the Ebola epidemic as the world's "highest priority", the UN launched a mission to prevent the global spread of Ebola.
Anthony Banbury, head of the UN Mission on Ebola Emergency Response (UNMEER), began a tour of the three hardest-hit nations in the Liberian capital Monrovia setting out an ambitious goal to eradicate the deadly virus.
"The only way we will end this crisis is if we end every single last case of Ebola so there is no more risk of transmission to anyone, and when that's accomplished, UNMEER will go home," he said.
The agency will work on health and education, Banbury said. But it will also make more vehicles available in the response and helping Ebola-free neighbouring countries defend themselves against a possible spread.
"The sooner UNMEER can end, the better for all of us. It's my hope that it will be as soon as possible because that means fewer lives will be lost," he told reporters.
President Ellen Johnson Sirleaf had told Banbury on his arrival in Liberia, the worst-hit nation with almost two-thirds of the 3,338 deaths in west Africa, that the virus had spread to all 15 of its counties.
The UN envoy said he was intent on contributing to "the highest priority for the international community -- for the whole world, not just the United Nations".
On Friday, he is to move on to Sierra Leone and then Guinea on Sunday.
- 'International crisis' -
US health officials were monitoring 100 people in Texas who had potential contact with a Liberian man diagnosed with Ebola. Four family members were also ordered to stay home.
The man -- the first person to be diagnosed with the deadly disease on US soil -- flew from Liberia and arrived in Texas September 20 to visit family. He fell ill on September 24, reportedly after helping a pregnant woman in Liberia who later died of Ebola. He is in serious but stable condition.
In a separate development, NBC television said a freelance cameraman working for the network in Liberia had caught the disease.
"He immediately quarantined himself and sought medical advice," NBC said. The 33-year-old American is to be flown back to the United States for treatment.
Ebola is spread through close contact with the bodily fluids of an infected person, and can only be transmitted when a patient is showing symptoms such as fever, aches, bleeding, vomiting or diarrhoea.
The Liberian government expressed "regret" on Thursday over the spread of Ebola from Monrovia to the US, adding that the incident had demonstrated "the clear international dimension of this Ebola crisis".
The incubation period for Ebola is between two and 21 days. Patients are not contagious until they start to have symptoms. But once the disease takes hold, it can lead to massive bleeding and fatal organ failure.
The World Health Organization said in its latest situation update there was still a "significant shortfall" in capacity in west Africa, with 1,500 more beds needed in Liberia and 450 in Sierra Leone.
Around 160 health professionals pledged by Cuba to Sierra Leone arrived Thursday, reported an AFP correspondent at the airport near Freetown.
- 'Terrifying' infection rate -
Meanwhile Doctors Without Borders, the global aid agency leading the response in west Africa, with 3,000 staff including some 250 Western volunteers, has criticised the inadequacy of international aid, saying it desperately needs medical teams rather than cash.
Britain asked for foreign help to battle Ebola in Sierra Leone, a former colony, on Thursday at a London conference gathering ministers, diplomats and health officials from around 20 countries and world organisations.
Sierra Leone President Ernest Bai Koroma, whose country has seen more than 600 deaths, was unable to attend after his plane broke down.
A charity, Save the Children, warned as the conference began that five people are being infected with Ebola every hour in Sierra Leone and demand for treatment beds is far outstripping supply.
If the current "terrifying" rate of infection continues, 10 people will be infected every hour with the deadly virus in the country by the end of October, the London-based group warned.
Britain has pledged Ģ120 million ($190 million, 150 million euros) to help build an estimated 700 treatment beds, fund new community treatment centres, support existing public health services and support aid agencies in Sierra Leone.
The United Nations has announced its first suspected victim of Ebola, a Liberian man who worked for the UN mission in Liberia and died of a probable but unconfirmed infection last week.
US oil giant ExxonMobil meanwhile said it had limited employee travel to the west African countries hit by Ebola, and delayed the start of an exploration well in Liberia.
Burkina Faso said cycling race Tour Du Faso, which was to be held from October 23 to November 2, would be suspended due to fears of Ebola.