United Nations Secretary-General Ban Ki-moon is "very much disappointed" that a humanitarian pause in fighting in Yemen didn't take hold, his spokesman said on Monday, after Saudi Arabia did not recognize the truce and continued air strikes.

A Saudi-led coalition of Arab states has been bombing the Iranian-allied Houthi rebel movement and army forces loyal to former Yemeni president Ali Abdullah Saleh since late March in a bid to restore exiled President Abd-Rabbu Mansour Hadi to power.

A week-long UN-brokered truce in fighting was meant to have begun on Saturday to allow the delivery of aid. Ban said on Thursday that Hadi had "communicated his acceptance of the pause to the coalition to ensure their support and collaboration."

However, Saudi Arabia said it had not been asked by Hadi, who had fled to Riyadh, to stop its campaign.

"Different people are saying different things. We very much stand by the commitments we have received for this pause," UN spokesman Stephane Dujarric told reporters.

"The Secretary-General is very, very much disappointed that the humanitarian pause did not take hold over the weekend in Yemen. We are continuing with contacts at various levels," Dujarric said.

The United Nations had said the Houthis, the General People's Congress and other parties had told UN special envoy Ismail Ould Cheikh Ahmed that the lull in fighting would be fully respected and there would be no violations from any of their combatants.

Still, there have been reports of fighting in breach of the pause conditions in Aden, Marib and Taiz, the main theaters of battle between local resistance movements, tribes, Islamist militants and the Houthis and Saleh's forces.

The United Nations has raised Yemen to its highest level humanitarian crisis, placing it alongside emergencies in South Sudan, Syria and Iraq.

More than 3,000 people have been killed and over a million displaced, and the United Nations said 21 million people need help, about 80 percent of the population.

"Despite the continued air strikes, despite the fighting, our humanitarian colleagues and their partners were able to distribute some vital aid to the desperate people of Yemen," Dujarric said.

Both sides had largely observed a five-day humanitarian truce brokered by the United Nations in May.

Yemen relies on imports, but a near-total blockade led by Saudi Arabia has slowed shipments to the war-torn Arabian Peninsula country to a trickle. The Arab coalition is inspecting shipments in a bid to thwart any arms deliveries to the Houthis.