GENEVA, Switzerland: The U.N. health agency says plans to ship cholera vaccine to Yemen are likely to be shelved over security, access and logistical challenges in the war-torn country.

Yemen's suspected cholera caseload has surged past 313,000, causing over 1,700 deaths in the world's largest outbreak. War has crippled Yemen's health system, depleted access to safe drinking water and put millions on the brink of famine.

Citing such complexities, World Health Organization spokesman Christian Lindmeier said Tuesday that shipping vaccines "has to make sense," and that they could be re-routed to places that "might need them more urgently."

Last month, the WHO and partners agreed to send 1 million doses of vaccine to Yemen.

WHO director-general Tedros Adhanom Ghebreyesus is to speak Wednesday to the U.N. Security Council on Yemen's cholera crisis.