Image copyright Getty Images Image caption Brazilian president Dilma Rousseff has said national mobilisation is needed to fight Zika

President Dilma Rousseff has called on the whole of Brazilian society to help combat the spread of the Zika virus, which has been linked to birth defects.

Ms Rousseff said national mobilisation was needed to eliminate the mosquitoes that spread the virus, and urged community groups and unions to help.

Zika is thought to cause a form of infant brain damage, microcephaly.

Three to four million people could be infected with Zika in the Americas this year, experts have warned.

Ms Rousseff rejected comments made by her health minister earlier this week, who said Brazil was badly losing the fight against the virus.

But Brazil is the country worst affected by the Zika outbreak, with 270 cases of microcephaly confirmed by the health ministry and 3,448 being investigated.

Concerns have arisen about Brazil's ability to safely host this year's Olympic Games in Rio de Janeiro. Thomas Bach, the head of the International Olympic Committee, has said steps are being taken to protect the event.

The IOC said it will issue guidelines later on Friday for athletes and visitors taking part.

Abortion petition

A group of Brazilian lawyers, activists and scientists is to ask the country's supreme court to allow abortions for women who have contracted the virus.

Abortions are illegal in Brazil, except in health emergencies or cases of rape or, since 2012, another brain condition known as anencephaly.

Media playback is unsupported on your device Media caption Deborah Diniz explains why she feels abortion laws need to change in Brazil

The new petition is to be delivered to the supreme court in two months' time. The BBC has learned that it argues that "the Brazilian state is responsible for the Zika outbreak" for not having eradicated the Aedes aegypti mosquito which carries it.

Brazilian women "should not be penalised for the consequences of flawed policies", it says.

The group behind the microcephaly supreme court plea also won the exception for anencephaly in 2012.

Debora Diniz, a law professor at Brasilia University, told the BBC the disease disproportionately affected the poor.

She said: "It is important to remember, when we talk about abortion and reproductive rights in general, that we have a social class split in Brazil - wealthy women will access safe abortion, legal or illegal, and poor women will go to the illegal market or continue to be pregnant."

No vaccine

Most people do not develop symptoms of the Zika virus but may pass the virus on to their children. There is no known cure or vaccine. The US says it hopes to begin human vaccine trials by the end of 2016.

Officials from the US National Institute of Health (NIH) said they had two potential Zika vaccines in development. One that is based on an experimental West Nile vaccine could be repurposed for Zika and enter clinical trials by the end of 2016, the NIH said.

WHO director general Dr Margaret Chan said Zika had gone "from a mild threat to one of alarming proportions". She has set up a Zika "emergency team" following the "explosive" spread of the virus.

The team will meet on Monday to decide whether Zika should be treated as a global emergency.

Zika was first detected in Uganda in 1947, but has never caused an outbreak on this scale. Brazil reported the first cases of Zika in South America in May 2015.

WHO officials said between 500,000 and 1.5 million people had been infected in Brazil, and the virus has since spread to more than 20 countries in the region.

Image copyright US CDC Image caption Aedes aegypti

What is the Zika virus?