The pro-government Arab coalition Sunday stepped up air strikes on Iran-backed rebels in Yemen and clashes raged on the ground as warring parties ignored a UN call to renew a fragile ceasefire.

The 72-hour ceasefire took effect just before midnight (2100 GMT) Wednesday to allow aid deliveries in Yemen, whose war has killed thousands of people and left millions homeless and hungry. It officially ended at midnight Saturday.

UN special envoy to Yemen, Ismail Ould Cheikh Ahmed, had appealed for a renewal of the ceasefire, saying humanitarian aid had during the truce reached areas that were earlier inaccessible.

But Yemeni Foreign Minister Abdulmalek al-Mekhlafi shrugged off the call as "useless", accusing the rebels of ignoring the ceasefire.

The truce was the sixth attempt since the Saudi-led coalition intervened in March last year to support the government of President Abedrabbo Mansour Hadi after Huthi rebels and their allies overran much of the impoverished country.

Ahmed urged "all parties to agree to its extension for at least another renewable 72 hours", in a statement posted on the envoy's Facebook page shortly before it expired.

The ceasefire was "largely holding despite reported violations from both sides in several areas", he said.

"We noted over the last days that food and humanitarian supplies were provided to several affected neighbourhoods and that UN personnel were able to reach areas that were previously inaccessible. We would like to build on this and we aim for a wider outreach in the next few days," he added.

- Cross-border shelling -

But shortly after the appeal, coalition warplanes on Sunday pounded positions in Sanaa of the Shiite rebels and their allies, renegade troops loyal to former president Ali Abdullah Saleh, military officials and rebel media said.

Rebel-controlled sabanews.net website counted nine air strikes on the capital Sunday.

The dawn raids also hit positions in Marib, east of the rebel-held capital, and the southwestern province of Taez, the officials said.

The intensity of air raids by the Saudi-led coalition had eased during the ceasefire.

"An extension (of the truce) would be useless, because even if we accept it, the other party does not make any commitment to respect the ceasefire," Mekhlafi told AFP.

"We respect the UN envoy's call for an extension, but in effect, there was no truce due to the violations" by the rebels, the foreign minister said.

Fighting on the ground was showing no signs of abating.

Fierce clashes raged in northern regions along the borders with Saudi Arabia over the weekend, killing at least 10 rebels and four Yemeni soldiers, military officials said.

Saudi civil defence also reported cross-border bombing which wounded a Yemeni resident of the southwestern city if Najran.

Later on Sunday, it said that more shelling from Yemen damaged two homes in the kingdom's Jazan region without causing casualties.

The UN envoy said Friday he was liaising with the parties in an attempt to extend the ceasefire in order "to create a conducive environment for a long-lasting peace" in Yemen.

Nearly 6,900 people have been killed in the conflict, more than half of them civilians, while an additional three million are displaced and millions more need food aid.

Hadi's government said on Sunday that nine people had died of cholera in second city Aden as the infectious disease spread across the war-torn country.

The last ceasefire attempt began in April and collapsed as UN-brokered peace talks hosted by Kuwait broke down in August.

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