The Saudi-led coalition launched air strikes Sunday on Yemen hours after Huthi rebels announced a three-day truce, with the UN chief condemning a surge in violence as the war enters its eighth year.

The raids targeted Sanaa, the rebel-held capital, according to Saudi Arabia's Al Ekhbariya TV, which tweeted "the start of air strikes on Huthi camps and strongholds in Sanaa" around midnight.

The attacks began shortly after the Iran-backed Huthis announced a three-day truce and offered peace talks on condition that the Saudis stop their air strikes and blockade of Yemen and remove "foreign forces".

Just a day earlier, the rebels had fired drones and missiles at 16 targets in Saudi Arabia, turning an oil plant near Jeddah's Formula One track into a raging inferno as aghast drivers looked on.

The flurry of attacks and diplomacy came as Yemen, the Arab world's poorest country, on Saturday marked seven years since the Saudi-led intervention against the Huthis, who seized Sanaa in 2014.

The conflict has killed hundreds of thousands of people directly or indirectly and displaced millions, creating what the United Nations calls the world's worst humanitarian crisis.

UN Secretary-General Antonio Guterres on Saturday condemned the sudden rise in hostilities.

He urged the warring parties to "immediately de-escalate" and reach a "negotiated settlement" with the help of Hans Grundberg, the UN's special envoy to Yemen.

The coalition's intervention has stopped the Huthis' advances in the south and east of the country but has been unable to push them out of the north, including Sanaa.

"Militarily, the war is now at stalemate," Elisabeth Kendall, a researcher at Oxford University, told AFP this week.