The World Health Organization (WHO) has suspended staff activity at its hubs in Houthi-held areas of Yemen, a directive seen by Reuters showed, in a move sources said aimed to pressure the group to be more transparent about suspected coronavirus cases.

War-ravaged Yemen, one of the countries most vulnerable to disease, is divided between the internationally recognised government temporarily based in the south and the Houthi group that ousted it from power in the capital, Sanaa, in late 2014.

The Saudi-backed government has so far reported 34 cases of the novel coronavirus with seven deaths in territory it controls, while the Houthis, who hold most large urban centres, have recorded just two cases with one death.

The WHO directive issued late on Saturday notified staff in Sanaa, the Red Sea port of Hodeidah, the northern province of Saada and central province of Ibb that "all movements, meetings or any other activity" for staff in those areas were paused until further notice.

The WHO has temporarily paused its movements in northern areas due to "credible threats and perceived risks which could have an impact on staff security", it said in response to a Reuters' query, adding that operations have not been suspended.

The United Nations is operating under the assumption that there is now full-blown transmission in Yemen, it said.

"We are competing for resources and supplies in the global market - and a country's 'priority status' in terms of who receives what for COVID-19 is directly linked to how many cases are in country and the need - it is the numbers," it said.

The U.N. has "systematically for weeks now" advised on case declaration and reporting, but the decision to do so rests with local authorities, the WHO added.

Three sources told Reuters the WHO had taken the measure to press Houthi authorities to report results of tests for COVID-19, the respiratory disease caused by coronavirus.

The Saudi-backed government has accused Houthi authorities of covering up an outbreak in Sanaa, a charge the group denies.

The WHO says it fears COVID-19 could rip through Yemen as the population has some of the lowest levels of immunity to disease compared with other countries. Minimal testing capacity has added to concerns.

The five-year war between a Saudi-led coalition and the Iran-aligned Houthi movement has shattered Yemen's health system and left its population weakened by hunger and disease.

Around 80% of the population, or 24 million people, rely on humanitarian aid and 10 million are at risk of starvation.