ADEN - Aid agencies warned Monday of a growing humanitarian crisis including food shortages in Yemen as Saudi-led warplanes hit rebel positions for a third week and rival forces clashed.

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.

Hadi accused Iran of fuelling a “campaign of horror and destruction” by the Huthi rebels, charging Tehran in an opinion editorial published in the New York Times of being “obsessed with regional domination”.

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 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.

The Huthis, who have joined with forces loyal to ex-president Ali Abdullah Saleh, advanced on Aden last month after seizing the capital Sanaa last year.

Western powers have also backed Hadi as Yemen’s legitimate ruler, while the United Nations has called for a resumption of talks. Heavy fighting in Aden on Sunday killed at least 13 civilians, 11 rebels and six pro-Hadi fighters, medical and military sources said.

Humanitarian groups have struggled to deliver aid and said Monday the situation in Aden was deteriorating rapidly. “Shops are closed. We have a problem of food,” said Marie-Elisabeth Ingres, Yemen representative of Doctors without Borders (MSF).

Metaz al-Maisuri, an activist in Aden, said basic services had ceased and there had been a “mass exodus” from the city. “Schools, universities and all public and private facilities have been shut,” he told AFP. “Residents’ lives have become very difficult and complicated... They can no longer obtain the food they need,” he said.

Adwaa Mubarak, a 48-year-old Aden resident, said: “We are unable to leave our houses to buy what we need because of the Huthi snipers.” She said several people were shot dead as they queued for bread.

UN Secretary General Ban Ki-moon warned from Doha on Sunday of a huge humanitarian crisis as “civilian casualties are mounting and public infrastructure is being destroyed”. Aid workers said Sanaa is also suffering, as air strikes hit rebel positions there and supplies dwindle.  “There is a food and water shortage. People are unable to move,” said Marie Claire Feghali, the Red Cross spokeswoman in Yemen.

The International Committee of the Red Cross flew more than 35 tonnes of medical aid and equipment into Sanaa on Saturday, after Friday’s first deliveries organised by the Red Cross and United Nations.

Thousands of foreigners have been trapped by the fighting, with the International Organization for Migration saying more than 16,000 are stranded.

Some evacuations have taken place, with Russia on Sunday saying it had evacuated more than 650 people by air and sea. The IOM said it had also flown a first planeload of 141 passengers out of Sanaa.

Riyadh has called on Iran to end its support for the rebels, accusing Tehran of assisting “criminal activities” in Yemen and giving the Huthis weapons and aid.

Iran has denied the allegation, and supreme leader Ayatollah Ali Khamenei has condemned the coalition’s raids on Yemen as “criminal”.

Hadi in his opinion piece accused the rebels of being Iran’s “puppets”. “Having a hostile government in a nation bordering the Bab al-Mandab strait - the highly trafficked shipping lane leading to the Suez Canal - is in no nation’s interest,” he wrote. “If the Huthis are not stopped, they are destined to become the next Hezbollah, deployed by Iran to threaten the people in the region and beyond.

Meanwhile, Iran on Monday urged the formation of a new Yemeni government and offered to assist in a political transition, comments likely to anger Saudi Arabia. “I had the privilege of participating in the Bonn Conference when we created the Afghan government. Actually we didn’t do it, the Afghans did ... We can do that in Yemen too,” Iranian Foreign Minister Mohammad Javad Zarif said in a speech during a two-day visit to Kazakhstan.

Meanwhile, Saudi Arabia’s military spending grew 17 percent in 2014 to $80.8 billion, data from the Stockholm International Peace Research Institute (SIPRI) showed on Monday, the biggest annual hike by any of the world’s top 15 military spenders.

Saudi Arabia launched air strikes last month on Houthi rebels in neighbouring Yemen, leading a regional coalition against fighters it says are backed by rival Gulf power Iran.

“While total world military spending is mostly unchanged, some regions, such as the Middle East and much of Africa, are continuing to see rapid build-ups that are placing an increasingly high burden on many economies,” said Sam Perlo-Freeman, Head of SIPRI’s Military Expenditure project.

“These increases partly reflect worsening security situations, but in many cases they are also the product of corruption, vested interests and autocratic governance.”

At $1.8 trillion, global military spending fell by 0.4 percent last year, down for the third consecutive year, SIPRI said. US and Western European cuts were mostly countered by hikes in Asia and Oceania, the Middle East, Eastern Europe and Africa. Spending in Latin America was roughly flat.

The Ukraine conflict made many countries close to Russia hike defence budgets, SIPRI said, reversing a previous trend for falling spending.

Ukraine increased spending by 20 percent last year and plans to more than double its military budget in 2015, SIPRI said.