Intense bombing by a Saudi-led coalition hit Yemen again Friday, three weeks into an air war against Iranian-backed rebels, as Al-Qaeda seized more ground in the chaos amid UN calls for peace.
Columns of smoke rose over an arms depot targeted by warplanes east of the capital Sanaa, witnesses said.
The facility belonged to the elite Republican Guard, which remains loyal to former president Ali Abdullah Saleh.
Renegade troops loyal to Saleh are allied with the Huthi rebels, whose sweeping advance forced President Abedrabbo Mansour Hadi to flee to Riyadh last month.
Following heavy overnight air strikes in the north, coalition aircraft also hit the presidential palace in the southern city of Taez, the witnesses said.
Coalition spokesman Brigadier General Ahmed al-Assiri said that "from this afternoon we have started operations in Taez".
Speaking in Riyadh, he added that there had been 100 sorties in Yemen on Thursday, indicating that there is no end in sight to the operation.
"This works needs patience, persistence and precision. We are not in a hurry... We have the time and we have the capabilities."
Air strikes on the southern port city of Aden killed a rebel, while at least 76 other people died in bombing and fighting around Aden and Taez, officials said.
The United Nations says hundreds of people have died and thousands of families fled their homes in the war, which has also killed six Saudi security personnel in border skirmishes.
UN chief Ban Ki-moon called for an immediate ceasefire and began the hunt for a new peace envoy to the country, where Al-Qaeda is expanding its territory.
Yemen "is in flames," he said Thursday, calling for an "immediate ceasefire in Yemen by all parties".
His remarks followed the resignation of his envoy Jamal Benomar, who had lost the confidence of Saudi Arabia and its allies. They accused him of being duped by the rebels.
The Moroccan diplomat had been instrumental in negotiating a deal that eased Saleh from office in February 2012 after a year of protests against his three-decade rule.
- Political process a 'must' -
Saudi Arabia's regional rival, Iran, renewed its calls for dialogue on Friday and said its foreign minister had spoken to the UN chief overnight.
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Ban said he was in the process of finding a new envoy "who can be immediately deployed" to seek a political solution.
"The Saudis have assured me that they understand there must be a political process," Ban said.
The Yemen conflict has sent tensions soaring between Saudi Arabia and Iran -- the foremost Sunni and Shiite Muslim powers in the Middle East.
Tehran is a key ally of the Huthis but denies arming them.
"This is not true," Iranian media on Friday reported Hossein Salami, deputy commander of the elite Revolutionary Guards, as saying.
Yemen has sunk further into chaos since the start of the air raids, most of which Western diplomats say have been carried out by Saudi Arabia itself.
Yemen is a front line in the US war on Al-Qaeda, which has exploited the growing turmoil to expand its control of areas in the southeast of the deeply tribal Arabian Peninsula country.
- Qaeda overruns Mukalla -
On Friday, Al-Qaeda overran a key army camp in the Hadramawt provincial capital Mukalla, seizing heavy weapons and consolidating their grip on the city, an official said.
Residents confirmed that the camp, which had remained loyal to Hadi, was taken "without resistance".
Despite the collapse of Hadi's government in Yemen, Washington has vowed to carry on its campaign against Al-Qaeda in the Arabian Peninsula.
Two suspected AQAP militants were killed in an apparent US drone strike in Shabwa province in the south overnight, a tribal source said.
The World Health Organization, in a new toll, says 767 people have died in Yemen's war since March 19 and more than 2,900 were wounded. The majority have been civilians.
The United Nations launched an urgent appeal for $274 million (253 million euros) to provide emergency aid for what was already the region's poorest country.
"Ordinary families are struggling to access health care, water, food and fuel -- basic requirements for their survival," UN Humanitarian Coordinator Johannes Van Der Klaauw said.
The White House said President Barack Obama will host leaders of the six-nation Gulf Cooperation Council on May 13-14 to discuss Yemen and other regional issues.
Meanwhile, a Norwegian journalist, detained in Huthi-controlled Sanaa in late March, has been freed and is on his way home, Oslo's foreign ministry said.