By Michelle Nichols

UNITED NATIONS (Reuters) - Liberia's national existence is "seriously threatened" by the deadly Ebola virus that is "spreading like wild fire and devouring everything in its path," the country's national defence minister told the United Nations Security Council on Tuesday.

Liberia is worst hit by West Africa's Ebola epidemic and will likely see thousands of new cases in coming weeks, the World Health Organisation (WHO) said on Monday. More than 1,000 people have already died in Liberia.

"Liberia is facing a serious threat to its national existence. The deadly Ebola virus has caused a disruption of the normal functioning of our State," said Liberian Minister of National Defence Brownie Samukai.

"It is now spreading like wild fire, devouring everything in its path. The already weak health infrastructure of the country has been overwhelmed," he told the 15-member council, adding that the initial international response was "less than robust."

U.N. special envoy to Liberia Karin Landgren told the council that at least 160 Liberian health care workers had contracted the disease and half of them had died. She described the spread of Ebola as "merciless" and warned that the reported cases and deaths in Liberia "understate Ebola's true toll."

"The speed and scale of the loss of lives, and the economic, social, political and security reverberations of the crisis are affecting Liberia profoundly," she said. "Liberians are facing their gravest threat since war."

Two wars between 1989 and 2003 killed about 250,000 people and led to a complete collapse of Liberia. It was carved up by warlords who often used child soldiers and fought over control of diamond and timber concessions.

U.N. peacekeepers were deployed to Liberia in 2003 and some 6,000 troops and police are currently there. The mission's mandate is due to be renewed by the Security Council this month and U.N. Secretary-General Ban Ki-moon has recommended a straightforward extension of three months, instead of one year, while the international community tackles Ebola.

The WHO said on Tuesday that it had recorded 4,293 cases in five West African countries as of Sept. 6. It said it still did not have new figures for Liberia. The outbreak began in Guinea and has spread to Liberia, Sierra Leone, Nigeria and Senegal.

An Ebola outbreak said to be unrelated to the one in West Africa has been reported in Democratic Republic of Congo, where Ebola was first identified in 1976.

Ebola is a haemorrhagic fever spread through body fluids such as the blood, sweat or vomit of those who are infected with the disease. Health care workers are among the most vulnerable to the disease. Liberia's Samukai said nine of Liberia's 15 counties are affected.

"The pandemic has mushroomed into a health emergency exceeding the government's response," he said."Liberia lacks the infrastructure, logistical capacity, professional expertise and financial resources to effectively address this disease."

The worst epidemic since the disease was discovered has killed at least 2,296 people.

"It is imperative that we as an international community get serious about addressing the public health, humanitarian and security effects of this outbreak," U.S. Ambassador to the United Nations, Samantha Power, said after the briefing.

"I don't think anybody can say right now that the international response to the Ebola outbreak is sufficient," said Power, who is president of the council for September. "Every organisation and every single member state in the international community needs to be looking at how we up our game."

Ban said he plans to hold a meeting on the international response to the Ebola crisis on the sidelines of the U.N. General Assembly later this month.

(Reporting by Michelle Nichols; Editing by Toni Reinhold)