More than 220,000 soldiers are being deployed across Brazil to warn people about the risks of the Zika virus.

Brazil is at the centre of an outbreak of the virus, which has been linked to a surge in babies being born with underdeveloped brains.

The country has 462 confirmed cases of the birth defect, called microcephaly, and is investigating thousands of suspected cases.

The nationwide offensive is part of Brazilian President Dilma Rousseff's declared war on the virus that has quickly spread across the Americas.

The government said 220,000 members of the armed forces accompanied by community health agents and mosquito control teams are taking part in the effort to educate the population on how to eliminate Aedes aegypti mosquitos - which carry the virus - breeding areas in and around their homes.

The government said troops will visit three million homes to hand out explanatory pamphlets.

It came as authorities said on Saturday that 5000 pregnant Colombian women are infected with the mosquito-borne Zika virus.

Cases of the virus now total 31,555, the national health institute said in a epidemiology bulletin, among them 5013 pregnant women.

As well as microcephaly, Zika, which has spread to more than 30 countries, has also been linked to neurological disease Guillain-Barre Syndrome (GBS).

The rare condition, in which the body's immune system attacks part of the nervous system, causes gradual weakness in the legs, arms and upper body and sometimes leads to total paralysis.

On Saturday the World Health Organization (WHO) said cases of GBS had risen in Brazil, Colombia, El Salvador, Suriname and Venezuela,

"In the context of the Zika virus outbreak, Brazil, Colombia, El Salvador, Suriname and Venezuela have reported an increase of GBS," the WHO said in a weekly report on Zika virus.

But it added: "The cause of the increase in GBS incidence observed in Brazil, Colombia, El Salvador and Suriname remains unknown, especially as dengue, chikungunya and Zika virus have all been circulating simultaneously in the Americas."

Total reported Zika cases increased by 23% over last week's figures, while the number of pregnant women with the virus was up 57.8 percent.

Much remains unknown about Zika, including whether the virus actually causes microcephaly.

Brazil is investigating the potential link between Zika infections and more than 4300 suspected cases of the condition, which is marked by abnormally small head size that can result in developmental problems.

There are so far no recorded cases of Zika-linked microcephaly in Colombia, the government has said. Officials are still examining figures from countries such as Brazil, but say Colombia can expect between 500 and 600 cases this year.

There is no vaccine or treatment for Zika, which causes mild fever, rash and red eyes. An estimated 80% of people infected have no symptoms.