More than half of all deaths have no recorded cause, making effective health monitoring and policymaking far more difficult, the World Health Organization (WHO) said on Wednesday.



However, improved collection of statistics meant that 27 million of the world's 56 million estimated deaths in 2015 were registered with a cause compared with only about a third in 2005, the U.N. health agency's latest global health report said.



The WHO said several countries, including China and Turkey, had made "significant strides" in data collection. In Iran, it said, 90 per cent of deaths are now recorded with details of the causes, compared with 5 per cent in 1999.



While things have improved significantly in recent years, many countries still do not routinely collect high-quality health data, Marie-Paule Kieny, the WHO's assistant director-general for health systems and innovation, said in a statement.



"If countries don't know what makes people get sick and die, it's a lot harder to know what to do about it," she said.



The WHO is working with countries to strengthen health information systems and improve data quality, she said.



This year's WHO report focused on the U.N. Sustainable Development Goals (SDGs), a set of internationally agreed targets adopted in 2015 which track issues such as health, climate, sanitation and economic inequality.



It found that while maternal and newborn death rates are declining, the 2015 global neonatal mortality rate was 19 per 1,000 live births and the under-five death rate was 43 per 1,000 live births. About 830 women died every day due to complications of pregnancy or childbirth in 2015, it said.



Looking at infectious diseases, it found that an estimated 2.1 million people were newly infected with HIV in 2015, 35 per cent fewer than in 2000.



There were an estimated 212 million malaria cases globally in 2015, the report found, and about 60 per cent of the population at risk of the mosquito-borne disease had access to an insecticide-treated net 2015, compared to 34 per cent in 2010.