Countries including the U.K., Australia and Taiwan have issued travel advisories for tourists to Singapore after the city-state announced a further increase in Zika cases.

Singapore's Ministry of Health confirmed 15 more cases of locally-transmitted Zika virus on Monday, bringing the total number of affected to 56.

The new cases involved people who live or work in the Sims Drive and Aljunied Crescent area, and were detected from testings of potentially infected persons, according to a government statement.

The various travel advisories issued Monday warn expecting mothers to exercise caution and defer all non-essential travel to Singapore.

The Zika virus is transmitted mainly by Aedes mosquitoes, and has been linked to a rare birth effect, known as microcephaly, in babies whose mothers suffered from the virus while pregnant. Symptoms include fever, skin rash, red eyes, muscle and joint pain, malaise or headaches.

There is currently no cure or vaccine to prevent Zika infection, and treatments are focused on relieving symptoms.

Malaysia, which shares a border with Singapore, Monday announced an increase of precautionary measures such as thermal scanners to detect fever at major entry points in the state of Johor and various airports, reported The Straits Times.

An average of nearly 296,000 people pass through the Johor-Singapore customs border daily, according to Malaysia's Immigration Department records.

About 3,600 premises in Singapore's affected regions were checked for mosquito breeding, and 36 mosquito breeding habitats were detected and destroyed, according to a joint Ministry of Health and National Environment Agency statement released on Monday.

The government has also been stepping up on precautionary measures such as thermal fogging, misting and indoor spraying of insecticides at inspected premises.

Singapore had reported a case of Zika in May, in a man who had been to Brazil, the country at the center of the global Zika outbreak.

Last week Hong Kong reported what was thought to be its first locally-transmitted Zika case but that person has since tested negative for the virus.

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