SANAA, Yemen — Thousands of people have been diagnosed with dengue fever in southern Yemen, where fighting has raged for months between Shiite rebels and their opponents, international organizations and health officials said Thursday.

The top health ministry official in the southern port city of Aden, al-Khadr Al-Aswar, told The Associated Press that at least 5,000 people have been diagnosed with the mosquito-borne virus. He said mountains of uncollected garbage, along with untreated sewage and heat, have contributed to the spread of the disease.

The World Health Organization said last week that at least 3,000 suspected cases have been reported since March in several provinces, including Ade, with three people dying from the disease. Dengue causes fever, headaches and skin rashes. Potentially lethal cases, mainly in children, involve abdominal pain, vomiting and difficulty breathing, according to the WHO.

The WHO said the last major Yemeni outbreak, with 1,500 confirmed cases, was in 2011 in the western Hodeida governorate.

The fighting in Yemen pits the Shiite rebels, known as Houthis, and military units loyal to former President Ali Abdullah Saleh against an array of forces, including southern separatists, local and tribal militias, Sunni Islamic militants and loyalists of internationally recognized President Abed Rabbo Mansour Hadi. A Saudi-led coalition backed by the United States began carrying out airstrikes against the Houthis and their allies in late March, but has made little progress in pushing them back.

The unrest has killed more than 1,000 civilians, displaced more than a million and led to severe shortages of food, water, fuel and electricity. The lack of fuel has put garbage trucks out of service, and the mounds of uncollected trash incubate mosquitoes that carry the disease.

U.N.-brokered talks are underway in Geneva, where mediators had hoped to secure a cease-fire in time for the Islamic fasting month of Ramadan, which began Thursday.