Pre-dawn raids hit several Houthi rebel military targets in east and south Sanaa, as well as the Houthi-controlled port city of Hodeida and the contested city of Taiz on Sunday. There was no immediate word on casualties.
Rebel-run television channel al-Masirah reported that Houthi rebels had launched a counterattack of artillery fire on government forces in Taiz.
Yemen descended into full-blown civil war between the Western and Saudi backed exiled government and Iranian allied Shiite Houthi rebels in March 2015, when Houthi fighters took control of the country’s capital.
Since then, more than 10,000 people have died, the UN says, more than three million people have been displaced, and the country is on the brink of famine thanks to the Saudi closure of Yemeni airspace and port blockades in the Gulf of Aden.
Saudi-led air strikes from March 2016 onwards have escalated the conflict and resulted in a sharp increase in civiilian deaths.
Western governments' sales of arms to the Kingdom have come under renewed scrutiny since a coalition bombing of a funeral hall earlier this month killed 140 civilians.
Human Rights Watch and other monitors say Saudi Arabia's military targeting systems are not sophisticated enough to avoid unneccessary harm to civilians, calling the funeral hall attack a war crime.
This week’s ceasefire - agreed to increase the flow of aid deliveries to desparate areas - was marred by accusations from both sides of violations. Pleas to extend it by another 72 hours from the UN’s special envoy to Yemen, Ismail Ould Cheikh Ahmed, appear to have failed as hostilities resumed.
Mr Ahmed is due to arrive in Sanaa later on Sunday to discuss a political resolution to the conflict with Houthi representatives.
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