War-battered Yemen has been hit with more than 460,000 suspected cholera cases so far this year -- a sharp rise from the 380,000 cases for all of 2018, the United Nations said Monday.

UN deputy spokesman Farhan Haq said the increased number of cases has led to 705 apparent cholera deaths since January, dramatically higher than the 75 deaths in the same period last year.

Haq said the spread of cholera across the country has been accelerated by recent flash flooding, poor maintenance of waste management systems and a lack of access to clean water for drinking or irrigation.

The United Nations and its partners are operating nearly 1,200 cholera treatment facilities across Yemen, but Haq said that "funding remains an urgent issue." The UN humanitarian appeal for $4.2 billion to help more than 20 million Yemenis this year is only 32 per cent funded.

The conflict in Yemen began with the 2014 takeover of the capital, Sanaa, by Iranian-backed Houthi Shiite rebels, who toppled the government of Abed Rabbo Mansour Hadi. A Saudi-led coalition allied with Hadi's internationally recognized government has been fighting the Houthis since 2015.

Saudi-led airstrikes have hit schools, hospitals and wedding parties and killed thousands of Yemeni civilians. The Houthis have used drones and missiles to attack Saudi Arabia and have targeted vessels in the Red Sea.

Civilians have borne the brunt of the conflict, which has killed over 10,000 people, created the world's worst humanitarian crisis, brought the Arab world's poorest country to the brink of famine and sparked the cholera outbreak.

Last month, the UN Security Council expressed deep concern at the gravity of the humanitarian situation and its continued deterioration since December 2018, including a serious resurgence of cholera.

UN humanitarian chief Mark Lowcock told the council in mid-June that 80% of Yemen's more than 24 million people "need assistance and protection, including 10 million who rely on food aid to survive." He said that figure was 50% higher than before the war, and added that for the first time in 2019 "assessments confirm pockets of famine-like conditions in dozens of places across Yemen."

He urged donors to be generous, saying funds were needed to prevent famine, and to prevent and respond to the cholera outbreak.