President Obama warned the US could face "bigger problems" as he criticised American politicians for failing to back his request for a $1.9bn (£1.25bn) fund to combat the Zika virus. On 20 May, he told media the Senate had only agreed to half of the required funding and Congress just a third.

"This is not something where we can build a wall to prevent," he said of the virus. "Mosquitoes don't go through customs, to the extent that we're not handling this thing on the front end, we're going to have bigger problems on the back end," Obama said.

President Obama said that even the $589m (£406m) that has been allocated for Zika research and prevention had been diverted from funds earmarked to tackle the threat of Ebola, which ravaged parts of West Africa, claiming more than 11,000 lives between December 2013 and January 2016.

Obama's comments came within hours of the US Centers for Disease Control and Prevention (CDC) announcing that the number of reported Zika infections in pregnant women within US territories had tripled in less than a week. Earlier this week, the CDC's website had listed 48 pregnant women were infected with Zika in the US. But on 20 May, the CDC announced the number of cases had jumped to 157.

The CDC's Chief of the Birth Defects, Dr Margaret Honein, told CNN that they were aware of "less than a dozen" babies or fetuses that have suffered consequences of Zika infection, but pointed out that most of the 157 pregnancies are ongoing, so it is not known how many babies will eventually be affected by the disease.

The Zika outbreak began nearly a year ago in Brazil. The country confirmed there are about 1,200 cases of microcephaly and considers most of these cases due to Zika infections.

Brazil has since spread to more than 20 countries in the Americas. On 20 May, World Health Organisation (WHO) announced that tests showed that a Zika outbreak in the African archipelago of Cape Verde is of the same strain as the one blamed for birth abnormalities in Brazil.

"The findings are of concern because it is further proof that the outbreak is spreading beyond South America and is on the doorstep of Africa," said WHO's Africa director, Matshidiso Moeti.