The death toll from Ebola has risen to 518, as the deadly virus continues to spread.
The World Health Organisation said 50 new cases and 25 deaths had been reported in Sierra Leone, Liberia and Guinea since July 3.
The increase in cases of Ebola in west Africa is a "cause for concern", but the risk to travellers remains "very low", Public Health England (PHE) said.
Around 779 cases have been reported in Guinea, Sierra Leone and Liberia, killing an estimated 481 people in the largest ever known outbreak of the disease.
PHE confirmed it has sent a number of laboratory and health staff to the region in a bid to bring it under control.
"The increase in cases and expansion into new areas are cause for concern, as this indicates that the outbreak is not yet under control," Dr Dilys Morgan, head of gastrointestinal, emerging and zoonotic diseases at PHE, said.
"The risk to travellers and people working in these countries of contracting Ebola is very low, but we have alerted medical practitioners about the situation in West Africa and requested they remain vigilant for unexplained illness in those who have visited the affected areas."
The death toll from the Ebola virus in Guinea, Liberia and Sierra Leone has risen to 467, out of 759 cases, according to the World Health Organization.
The figures include confirmed, probable and suspected cases.
A previous WHO update put the death toll at 399 as of June 23, out of 635 cases.
The World Health Organisation has warned West Africa to prepare for the possibility of the deadly Ebola virus spreading to Mali, the Ivory Coast and Senegal.
"We want other countries in West Africa to be ready - bordering countries, Ivory Coast, Mali, Guinea Bissau - to prepare themselves in case people affected with the disease may be also travelling," WHO medical officer Dr. Pierre Formenty said in Geneva today.
The WHO is not considering the recommendation of travel or trade restrictions on the three countries already affected by the epidemic - Guinea, Sierra Leone and Liberia.