The head of the International Committee of the Red Cross began a three day visit to Yemen on Saturday to assess the dire humanitarian situation in the war-torn country.
Peter Mauer flew into the rebel-held capital Sanaa where he was welcomed by Huthi rebel officials, an AFP correspondent reported.
Mauer is to hold talks with Huthi leaders and with their allies from the General People's Congress party of ousted president Ali Abdullah Saleh.
The ICRC said in a statement ahead of the visit that his trip would focus on the "dire humanitarian situation" in Yemen and that he would hold talks with unidentified "leading officials".
More than four months of ferocious fighting in Yemen between the rebels and loyalists of the exiled government have devastated the impoverished country.
The loyalists have been backed by air strikes and an air and sea blockade by a Saudi-led coalition.
The United Nations says that nearly 4,000 people have been killed, half of them civilians, while 80 percent of the 21 million people are in need of aid and protection.
The ICRC says that 1.3 million Yemenis have been displaced by the conflict.
"The human cost of this conflict is such that no family in Yemen today has been left unaffected," Mauer said in a statement ahead of his visit.
"We are particularly concerned about attacks on medical facilities and personnel. Moreover, deliveries of food, water and medicine must be facilitated not hampered," he added.
It was not clear if Mauer will visit loyalist-held second city Aden during his trip. The southern port has been devastated by the fighting.
Last month, the government announced it had "liberated" Aden, the last refuge of President Abedrabbo Mansour Hadi before he went into exile with his government in neighbouring Saudi Arabia in March.