Ebola is threatening the very existence of Liberia as the virus spreads like “wildfire”, the country’s defence minister, Brownie Samukai, has warned, following a World Health Organisation assessment that the worst is yet to come.

After predicting an “exponential increase” in infections across west Africa, the WHO warned that Liberia, which has accounted for half of all deaths, could initially only hope to slow the contagion, not stop it.

“Liberia is facing a serious threat to its national existence,” Samukai told a meeting of the UN security council on Tuesday. The disease is “now spreading like wildfire, devouring everything in its path”, he said.

The latest death toll is 2,296 out of 4,293 cases in Liberia, Sierra Leone, Guinea and Nigeria as of 6 September. Nearly half of all infections have occurred in the past 21 days. The latest WHO figures underscore Ebola’s asymmetric spread, as it travels through densely populated communities with decrepit health facilities and poor public awareness campaigns.

The WHO’s epidemiology chief, Sylvie Briand, said on Tuesday that the goal in Senegal and Nigeria was to stop transmission completely. Senegal has announced only one infection, while Nigeria has recorded 19 infections and eight deaths. The Democratic Republic of the Congo is battling a separate outbreak, which has killed 32 people in a remote north-western region.

“But in other locations, like Monrovia, where we have really wide community transmission, we are aiming at two-step strategies,” Briand said in Geneva. “First, to reduce the transmission as much as possible, and, when it becomes controllable, we will also try to stop it completely. But at this point in time we need to be pragmatic and try to reduce it in the initial steps.”

Before the outbreak, Liberia had only one doctor for every 100,000 patients in a population of 4.4 million. In Montserrado county, which contains Monrovia, there are no spare beds at the few Ebola treatment sites operating, the WHO said. It described how infected people were being driven to centres only to be turned away, return home and create “flare-ups” of deadly fever in their villages. It said 1,000 beds are needed – far more than the 240 operational and 260 planned.

Guinea’s president, Alpha Conde, described Ebola as a “war” his nation – with 555 dead so far – needed to win. He criticised neighbouring countries, including Ivory Coast and Senegal, for shutting their borders, and airlines for suspending flights to affected countries. “They forget that when you close borders, people just go through the bush. It’s better to have official passages of transit,” he said.

The African Union commission chief, Nkosazana Dlamini-Zuma, also called for travel bans to be lifted “to open up economic activities”.

In Gambia, customs officials said they had closed the borders to Guineans, Liberians, Nigerians and Sierra Leoneans – though not to neighbouring Senegal. “We are also advising Gambians intending to travel to these countries to cancel their trips, but any Gambian who fails to heed our advice, we will not allow you in the country if you return,” Ebrima Kurumah, a health officer posted at the border with Senegal, told AFP.