Air raids, naval shelling and ground fighting shook Yemen on Sunday in some of the most widespread combat since a Saudi-led alliance intervened last month against Iranian-allied Houthi militia who have seized large tracts of the country.
There were at least five air strikes on military positions and an area near the presidential palace compound in the Houthi-held capital Sanaa at dawn on Sunday, while warships pounded an area near the port of the southern city of Aden, residents said.
"The explosions were so big they shook the house, waking us and our kids up. Life has really become unbearable in this city," a Sanaa resident who gave his name as Jamal told Reuters.
The strikes on Sanaa were the first since the Saudi-led coalition said last week it was scaling back a campaign against the Houthis. But the air raids soon resumed as the Houthis' nationwide gains had not been notably rolled back, and there has been no visible progress toward peace talks.
Saudi Arabia, the world's top oil exporter and arch Sunni Muslim regional adversary of Shi'ite Muslim Iran, feels menaced by the Shi'ite Houthi advance across Yemen since last September, when the rebels captured the capital.
The Houthis later forced President Abd-Rabbu Mansour Hadi into exile. The Saudi-led intervention aims to restore Hadi and prevent Yemen disintegrating as a state, with al Qaeda militants thriving in the chaos and one of the world's busiest oil shipping lanes off the Yemeni coast at risk.
Abu Dhabi's Crown Prince Sheikh Mohammed bin Zayed al-Nahyan visited King Fahd airbase in Saudi Arabia's Taif on Sunday and reaffirmed his country's commitment to the Saudi-led coalition.
"Our only choice is victory in the test of Yemen," the official WAM news agency quoted him as saying.
Fighters loyal to former president Ali Abdullah Saleh have been battling alongside the Houthi rebels.
In London, Yemeni Foreign Minister Riyadh Yaseen rejected a call for peace talks issued by Saleh on Friday and said the Saudi-led military operation had not ended.
"These calls are unacceptable after all of the destruction Ali Abdullah Saleh has caused. There can be no place for Saleh in any future political talks," Yaseen told a news conference.
"There will be no deal with the Houthis whatsoever until they withdraw from areas under their control," Yaseen said.
Eyewitnesses in Aden said foreign warships shelled Houthi emplacements around the city's main commercial port and dockyard, the first time they had been targeted.
Aden residents reported heavy clashes between local armed militia from Yemen's Sunni south and Houthis backed up by army units loyal to Saleh.
Sources in the militia said they retaliated for the first time with tank and Katyusha rocket fire. Air strikes backed up local militia in clashes near Aden's international airport.
In the southern province of Dalea, militia said they had fought for hours to retake several rural districts from the Houthis with the help of air strikes. The fighting left around 25 Houthis and six local militiamen dead.
A grouping of armed tribesmen and Sunni Islamist fighters in the strategically important central Yemeni city of Taiz took back several districts from the Houthis in heavy fighting, according to residents there.
Medics reported that four civilians were killed when a rocket landed in a street and shelling damaged a main hospital.
The battlefield setbacks for the Houthis occurred in an area they held largely unopposed for more than a month, and suggest that the air campaign has emboldened armed opposition groups.
Other air strikes hit Houthi bastions in Saada province along Yemen's northern border with Saudi Arabia, and Saudi ground forces also shelled the city of Haradh in neighbouring Hajja province, residents said.
Iran's navy chief said on Sunday that it would keep warships in the Gulf of Aden for at least several months, a stance that could harden U.S. concerns about Tehran trying to supply advanced weapons to the Houthis.
Admiral Habibollah Sayyari, quoted by the state news agency IRNA, said the ships had deployed to protect shipping routes against piracy. The Islamic Republic denies giving military support to the Houthis.
The United States sent an aircraft carrier and a missile cruiser to support seven US warships already near the Gulf of Aden this week, and warned Iran not to send weapons to Yemen that could be used to threaten shipping traffic.