SANAA, Yemen — Attempts to ease fighting in Yemen appeared to falter Thursday, as Shiite rebels pressed an offensive in the south and a Saudi Arabia-led coalition intensified its airstrikes less than two days after it said it was scaling back the campaign.

All sides have declared their willingness to enter talks, but none has taken any steps to end the conflict that has killed more than 1,000 people.

Still, the head of U.N. operations in Yemen said that a renewal of such talks is “inevitable,” and behind-the-scenes diplomatic efforts could bring results in the coming weeks.

The battle in the Arab world’s poorest country pits the Iranian-backed rebels known as Houthis and their allies – military units loyal to former President Ali Abdullah Saleh – against the Saudi-led coalition and the forces of President Abed Rabbo Mansour Hadi. Although Hadi is the internationally recognized leader, he was forced to flee his southern stronghold of Aden last month as the Houthis advanced toward the port. He is in the Saudi capital of Riyadh.

Western governments and the Sunni Arab countries in the coalition say the Houthis get their arms from Shiite powerhouse Iran. Tehran and the rebels deny that, although the Islamic Republic has provided political and humanitarian support to the Shiite group.

Warplanes hammered Aden, hitting hotels and a police station occupied by the Houthis and their allies. Heavy strikes also hit positions in five other cities, many of them gateways to Aden, officials said.

At least six airstrikes targeted an air base, a military camp, and weapon caches in the western port of Houdida. In the western city of Taiz, jets bombed the headquarters of Battalion 35, led by pro-Saleh commanders. In the nearby city of Ibb, the planes targeted educational facilities suspected of storing weapons, officials said.

Rebel reinforcements were bombed in the central province of Marib, while in the city of Dhale, another gateway to the south, airstrikes targeted suspected weapons depots and assembly points for fighters. Residents of Dahle said the city was being shelled by the Houthis and forces loyal to Saleh, Yemen’s longtime authoritarian leader who was a staunch U.S. ally.

On Tuesday, Saudi Arabia announced an end to the first phase of its coalition’s month-old air campaign against the Houthis. The Saudis said a new phase called “Renewal of Hope” was beginning, focused on diplomacy, protecting civilians, counterterrorism and halting future military actions by the Houthis.