* Warns consequences could be "catastrophic"
* Worst Ebola outbreak yet has killed 729 people
* Emergency meeting of leaders in Conakry on the outbreak
* Nigeria quarantines mortuary with body from Liberia (Adds two suspected cases in Nigeria cleared)
By Saliou Samb
CONAKRY, Aug 1 (Reuters) - An outbreak of the deadly Ebola virus in West Africa is out of control but can be stopped with more resources and tougher measures, World Health Organization chief Margaret Chan said on Friday.
The outbreak is the worst since the disease was discovered in the mid-1970s, with 729 deaths in four different countries.
"This outbreak is moving faster than our efforts to control it," Chan told the presidents of Guinea, Liberia and Sierra Leone at an emergency meeting in Guinea's capital Conakry.
"If the situation continues to deteriorate, the consequences can be catastrophic in terms of lost lives but also severe socio-economic disruption and a high risk of spread to other countries," she said, according to a WHO transcript.
But the outbreak could be stopped and the public was not at high risk of infection, she said.
Governments might need to restrict population movements and public gatherings, and use the police and civil defence forces to guarantee the security of response teams, she said.
With healthcare systems struggling to cope, more than 60 medical workers have lost their lives, hampering efforts to tackle the disease.
Two Americans working for aid group Samaritan's Purse who contracted the disease in Liberia were in a serious condition and would be medically evacuated by early next week, the organisation said.
Liberia has put in place measures including closing all schools and some government departments as well as possibly quarantining affected communities. Sierra Leone declared a state of emergency and called in troops to isolate Ebola victims.
However, the leader of Guinea's Ebola taskforce said his country would not be following these moves.
"Some measures taken by our neighbours could make the fight against Ebola even harder," Aboubacar Sidiki Diakité told Reuters, citing in particular the closure of schools.
"When children are not supervised, they can go anywhere and make the problem worse."
The outbreak has prompted some international organisations to withdraw. The U.S. Peace Corps has said it was withdrawing 340 volunteers from Liberia, Sierra Leone and Guinea. Samaritans Purse said on Friday it would complete the evacuation of its 60 international staff from Liberia over the weekend and WaterAid said on Friday it was suspending its operations there as well.
The WHO is launching a $100 million response plan and the United States is providing material and technical support to the three countries. Further assistance will be discussed at a meeting in Washington next week.
Chan said she was taking personal responsibility for coordinating international response efforts and mobilising the vast support needed to fight the virus.
The WHO has convened an emergency committee on Aug. 6-7 to decide if the outbreak constitutes a public health emergency of international concern and to recommend measures to tackle it.
"The demands created by Ebola in West Africa outstrip your capacities to respond," Chan told the presidents.
Chan said cultural practices such as traditional burials and deep-seated beliefs were a significant cause of the spread and a barrier to containment and needed to change.
In the final stages, its symptoms include external bleeding, internal bleeding, vomiting and diarrhoea - at which point Ebola becomes highly contagious.
Several healthworkers have been attacked and families often prefer to hide victims rather than take them to clinics.
On Friday, the government of southeastern Nigeria's Anambra state quarantined a mortuary where the body of a Nigerian man who died in Liberia had been left a day earlier. They also quarantined anyone who had had contact with his body.
"We are conducting pathological tests on cause of death," Anambra state government secretary Oseloka Obaze told Reuters.
Two people who had been quarantined in Lagos because they showed symptoms after coming into contact with the city's first Ebola victim were released on Friday, after they tested negative, Lagos state health commissioner Jide Idris told a news conference.
The haemorrhagic virus can kill up to 90 percent of those infected, though the fatality rate in this epidemic is about 60 percent. (Additional reporting by Tom Miles in Geneva, Tim Cocks and Oludare Mayowa in Lagos, Anamesere Igboeroteonwu in Onitsha, and Misha Hussain, Writing by Tim Cocks and Felix Bate; Editing by Daniel Flynn and Alison Williams)