Saudi-led warplanes launched dawn raids Saturday against Shiite rebels in Yemen's southern port city of Aden, the military said, hours after peace talks in Geneva ended without agreement.
At least 15 air strikes rocked the northern, eastern and western approaches to Aden, said a pro-government military source.
"The objective is to close the noose around the Huthi rebels in Aden and assist the popular resistance committees" loyal to exiled President Abedrabbo Mansour Hadi, the source said.
He said the rebels shelled several Aden neighbourhoods, killing four people and wounding several others, a toll confirmed by hospital officials.
The violence came hours after the UN's special envoy for Yemen, Ismail Ould Cheikh Ahmed, announced Friday in Geneva that talks between the warring sides ended without agreement.
"I won't beat around the bush. There was no kind of agreement reached," the Mauritanian diplomat told reporters in the Swiss city.
The rebels, backed by fighters loyal to ousted president Ali Abdullah Saleh, have overrun much of the Sunni-majority country, challenging the government's legitimacy and prompting Abedrabbo to flee to Saudi Arabia.
A coalition led by the oil-rich Gulf nation has carried out air strikes against the Huthis and their allies since March 26.
More than 2,600 have been killed in the fighting which has also left 80 percent of the population -- 20 million people -- in need of urgent humanitarian aid, according to UN estimates.
Aid groups and the UN say a dire humanitarian crisis is unfolding, and have appealed on all sides to stop fighting to allow them to move supplies to Yemen and distribute them to the needy.
The situation is particularly tragic in Aden, where residents have complained of food and water shortages, while medics speak of a rapidly deteriorating health situation and the spread of disease.
A boat laden with supplies, including flour, that was due to dock in Aden this week had to divert course to Hodeida in western Yemen due to the fighting, Aden's deputy governor Nayef al-Bakri said.
Bakri accused the Huthis of deliberately forcing the vessel, chartered by the UN's World Food Programme, to change course to Hodeida where they control the port to punish the people of Aden.
"They want to deprive Aden's residents, who have been resisting their presence, from this aid," he said.