Saudi-led coalition warplanes bombed Yemen on Wednesday despite an announcement by Riyadh that it was ending its campaign of airstrikes, while renewed fighting erupted on the ground between rebels and forces loyal to the exiled president.
The continued hostilities suggested how tough it may be to achieve a lasting diplomatic solution to conflict in the country.
Saudi Arabia's announcement Tuesday that it would suspend airstrikes against the Houthi rebel movement drew positive responses from both the White House and Iran, which supports the Houthis, as well as fresh calls for peace talks and for urgent deliveries of humanitarian aid.
But hours later, airstrikes and ground fighting resumed and the International Red Cross described the humanitarian situation as "catastrophic." The Houthi rebels said it wanted a return to United Nations peace talks, but only after a complete halt to the bombing.
Houthi fighters meanwhile captured an army base loyal to President Abed Rabbo Mansour Hadi in the city of Taiz. A Saudi airstrike hit the headquarters shortly afterwards, residents said. Coalition planes later hit rebel positions in southern Yemen with 12 more airstrikes, residents said.
Also in southern Yemen, pro-Hadi militiamen fought against the Houthis and their army allies loyal to powerful ex-President Ali Abdullah Saleh, and residents in the port of Aden reported tank shelling and automatic gunfire.
Southerners and Houthis also clashed on Wednesday around the southern town of Dalea, a hotbed of southern separatism that has changed hands several times in the conflict.
The southern movement brings together southern civilians, former army officers and members of a southern secessionist movement to oppose the Houthis, who are fighting alongside troops loyal to Saleh.
Saleh himself welcomed Saudi Arabia's announcement and called for the renewal of political dialogue, according to a statement on his Twitter account.
"We hope that everybody will return to dialogue to solve and treat all the issues," Saleh, a powerful ally of the Houthis, said in the message, which was also posted on his Facebook page.
Saudi Arabia said on Tuesday that it was ending airstrikes against the Houthis, whose seizure of swathes of Yemen in recent months has stirred Saudi fears that Iran is acquiring decisive influence in a country Riyadh sees as its backyard.
Saudi Arabia said a new phase called "Operation Restoring Hope" would now begin in which political, diplomatic and military action would be combined, but the main focus would be on the political process.
Iran called for all sides in Yemen's conflict to start negotiations, saying long-term peace was possible.
"History has demonstrated that military intervention is not a proper response to these crises and will instead exacerbate the situation," Iran's President Hassan Rouhani said at an Asian-African conference in Jakarta.
The United States and Saudi Arabia have accused Iran of arming the Houthis, though the extent of Tehran's support for the movement has never been fully established.
A Gulf official told Reuters that the new phase would see a downscaling of military activity by the Saudi-led coalition with no further bombing of fixed military targets.
On the political front, the official said, there was movement toward a dialogue, and that both Saleh's followers and the Houthis should have a voice in the discussions.
Saleh welcomed the Saudi announcement and called for talks, while the Houthis have yet to react beyond calling for mass protests against the Saudi "aggression."
A Hadi official told Reuters that the warring parties were discussing a seven-point peace plan offered by neighboring Oman, which has stayed neutral in the conflict, involving the reinstatement of Hadi's government and a Houthi withdrawal from leading cities, both previously non-starters for the group.
The White House on Wednesday said Yemen remained unstable and much more work needed to be done in the region on a diplomatic solution, despite the declared halt to the Saudi-led bombing.
Meanwhile, the conflict has created a desperate shortage of food and other supplies in Yemen, where sea and airports are closed. The World Health Organization said Tuesday that 944 people were reported killed and 3,487 wounded in Yemen in the four weeks up to April 17.
Leading Houthi figure Mohammed al-Bukhaiti said on Tuesday that the United States was guilty of worsening a "siege" of the country by sending warships to the waters off Yemen.
The U.S. said Monday that an aircraft carrier and guided-missile cruiser had gone there to join seven other U.S. warships already in the area.
The Pentagon said the ships were there to ensure freedom of navigation through the area, which is vital to oil shipping and access to the Red Sea and the Suez Canal.
It said the ships were also watching a flotilla of Iranian cargo vessels that had approached Yemen. The U.N. Security Council has imposed an arms embargo on the Houthis, and the Saudi navy has imposed a naval blockade around the country.
President Barack Obama warned Iran on Tuesday not to send weapons to Yemen that could be used to threaten shipping traffic in the region.
"What we've said to them is that, 'If there are weapons delivered to factions within Yemen that could threaten navigation, that's a problem,'" he said.
Al Jazeera and Reuters