In Riyadh, Yemen's Prime Minister Khaled Bahah was sworn in as vice president at the country's embassy in front of exiled President Abedrabbo Mansour Hadi, a day after his appointment, in a move welcomed by Yemen's Gulf neighbours.
Yemen's main southern city of Aden saw the heaviest fighting overnight, with medics and military forces saying at least 30 people were killed in clashes between rebels and supporters of Hadi.
Residents said warplanes from a Saudi-led coalition of countries pounded the rebel-held presidential complex and other positions in Aden, Hadi's last refuge before he fled to neighbouring Saudi Arabia as the air war began on March 26.
Saudi Arabia has accused Iran, the main Shiite power, of backing the rebel offensive and rallied support from regional allies for the coalition.
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Western powers have also backed Hadi as Yemen's legitimate ruler, while the United Nations has called for a resumption of UN-brokered talks aimed at bringing stability to the deeply divided country.
Heavy fighting in Aden last night left at least 13 civilians, 11 rebels and six pro-Hadi fighters dead, medical and military sources said.
"Shops are closed. We have a problem of food," said Marie-Elisabeth Ingres, the Yemen representative of Doctors without Borders (MSF).
Metaz al-Maisuri, an activist living in Aden, said basic services had stopped and there had been a "mass exodus" of civilians from the city.
"Schools, universities and all public and private facilities have been shut due" to the violence, he told AFP.
"Residents' lives have become very difficult and complicated... They can no longer obtain the food they need," he said.
"Our living conditions are bad. Bakeries are shut," she said, alleging that several people have been shot dead as they queued to buy bread.
UN Secretary General Ban Ki-moon warned from Doha yesterday that the escalation in fighting was leading to a huge humanitarian crisis in Yemen as "civilian casualties are mounting and public infrastructure is being destroyed."
The UN chief said more than 600 people had been killed and 2,000 injured so far.