Jamaica has ordered an immediate ban on people who have traveled through the Ebola-affected countries of Liberia, Guinea, and Sierra Leone, joining a growing number of states to impose such restrictions.

The ministry of national security said in a statement on Thursday that the ban covered "certain persons traveling directly or indirectly, from or through" those West African countries, where nearly 4,500 people have died of the disease.

News of the ban comes as opposition Republican politicians in the United States called on President Barack Obama to impose a similar ban, after two nurses who cared for Liberian patient Thomas Eric Duncan contracted the virus. Duncan later died of the disease.

Aside from Jamaica, another South American country, Guyana, said it had denied entry to citizens from the West African states, as well as Nigeria, for the past five weeks. Trinidad and Tobago, Colombia and St. Lucia took similar steps earlier this week.

Obama has so far resisted the call for a ban, saying on Thursday that experts have told him "a flat-out travel ban is not the way to go" because current screening measures on travelers are working.

At a White House meeting, Obama said he is considering appointing an Ebola "czar" as the lead US coordinator in the effort to contain the virus. He also signed an order calling up military reservists to help the government's anti-Ebola operation.

Earlier on Thursday, Thomas Frieden, director of the US Centers for Disease Control and Prevention, cautioned Congress members that a ban could only make the crisis worse.

He said some West Africans have US passports, and that others could come into the country without revealing their point of origin, making it harder to trace them.

'Burning building'

Closing national borders to people from countries hit hardest by the Ebola outbreak is "not an effective strategy" for stopping the deadly disease, the president of the World Bank said on Thursday.

There is only one way to end the Ebola crisis, which is to stop the spread of the disease in its origin, the World Bank's Jim Yong Kim told the Reuters news agency.

"All this talk about closing our borders ... it's as if you were in a burning house, in your room, and you start putting wet towels under the door to keep the smoke from coming in," Kim said.

The World Health Organization (WHO) has said it is focusing on 15 African countries to stop the disease.

Meanwhile, the European Union health ministers agreed on Thursday to try to improve the systems put in place by West African nations to screen departing passengers for Ebola, but disagreed on the need to check travellers arriving in their own countries.

France said on Wednesday it would begin screening air passengers for Ebola if they arrive on flights from regions hit by the disease, following similar decisions by Britain and the Czech Republic. But other EU governments have made no such move, as WHO regulations do not require screening.

On Thursday, Dr. Isabelle Nuttall, a WHO director, said that the outbreak is still out of control, and that the death toll will rise this week to more than 4,500 from the 9,000 infected patients.

"Our data shows that cases are doubling every four weeks," she said, adding that cases were growing in Guinea's capital Conakry, while data-gathering in Liberia, which has a significant under-reporting of cases, make it hard to draw any conclusions there.