Mogadishu (AFP) - Tens of thousands of Somali refugees have fled back home from war-torn Yemen since an upsurge in fighting in March, the UN said Tuesday, adding to three million already in need.

The refugees, who originally fled hunger and conflict in Somalia before being caught up in war in Yemen, have largely crossed the Gulf of Aden by boat to the Horn of Africa country's northern Somaliland and Puntland regions.

"Since March 2015, close to 29,000 people have arrived in Somalia from Yemen, 90 per cent of whom are Somalis with more expected to arrive in the coming months," according to the UN Office for the Coordination of Humanitarian Affairs (OCHA).

"More people fleeing the conflict in Yemen is increasing the burden on already limited basic services," OCHA said, adding that those who arrived had been helped with food and basic goods.

Over 1.1 million people are already displaced across Somalia, fleeing their homes to due to conflict, drought, hunger or floods, and three million people are in need of aid, the UN said, mainly in Somalia's southern regions, where Islamist rebels are fighting government and African Union troops.

Yemen has been rocked by months of fighting between Huthi rebels and forces loyal to President Abedrabbo Mansour Hadi, who have received air support from a Saudi-led coalition.

Almost 10,000 Yemenis have also arrived in the small state of Djibouti since late March, according to the UN.

Meanwhile thousands of Ethiopians and other migrants continue to travel in the opposite direction to war-torn Yemen, many of them tricked by smugglers into believing the fighting there is over.

The UN said last month that over 10,000 migrants had arrived in Yemen since air strikes began in March.