"The large majority are Ethiopians," Van Der Klaauw told journalists in Geneva, adding that Somalis, Eritreans and migrants of other nationalities were also among those heading to Yemen.
Many were economic migrants intending to travel to Saudi Arabia, he said, having crossed the Gulf of Aden by boat.
"Many are tricked into making the journey by smugglers who tell them that the conflict is over and all is safe in Yemen," the UN's refugee agency, the UNHCR, said in a statement.
Some Somalis, however, make the journey knowing how violence-wracked Yemen is, judging it worth risking the danger to escape a country where Shebab militants are fighting to overthrow the internationally-backed government.
The agency said it was launching "mass information campaigns" in Somalia's autonomous Puntland region and the self-declared independent Somaliland area in the north, to discourage people from crossing over.
The UN declared its highest-level humanitarian emergency in Yemen at the beginning of this month.
The UN says the conflict has killed more than 3,200 people, about half of them civilians, since late March.
More than 21.1 million people -- over 80 percent of Yemen's population -- need aid, with 13 million facing food shortages, while access to water has become difficult for 9.4 million people.
Van Der Klaauw said a convoy transporting aid from the UNHCR and the World Health Organization arrived in the southern Yemeni city of Aden on Saturday.
"It was the first time that we got a convoy into Aden for weeks," he added.
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Many were economic migrants intending to travel to Saudi Arabia, he said, having crossed the Gulf of Aden by boat.
"Many are tricked into making the journey by smugglers who tell them that the conflict is over and all is safe in Yemen," the UN's refugee agency, the UNHCR, said in a statement.
Some Somalis, however, make the journey knowing how violence-wracked Yemen is, judging it worth risking the danger to escape a country where Shebab militants are fighting to overthrow the internationally-backed government.
The agency said it was launching "mass information campaigns" in Somalia's autonomous Puntland region and the self-declared independent Somaliland area in the north, to discourage people from crossing over.
The UN declared its highest-level humanitarian emergency in Yemen at the beginning of this month.
The UN says the conflict has killed more than 3,200 people, about half of them civilians, since late March.
More than 21.1 million people -- over 80 percent of Yemen's population -- need aid, with 13 million facing food shortages, while access to water has become difficult for 9.4 million people.
Van Der Klaauw said a convoy transporting aid from the UNHCR and the World Health Organization arrived in the southern Yemeni city of Aden on Saturday.
"It was the first time that we got a convoy into Aden for weeks," he added.
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