The Saudi-led coalition has stepped up airstrikes on Iran-backed rebels in Yemen and clashes rage on the ground as warring parties ignore a UN call to renew a fragile ceasefire.

The 72-hour ceasefire took effect just before midnight on 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 on Saturday.

The 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. However, Yemeni foreign minister Abdulmalik al-Mekhlafi shrugged off the call as “useless”, accusing the Houthi 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 Abed Rabbo Mansour Hadi after Houthi rebels and their allies overran much of the impoverished country.

In a statement posted on Ahmed’s Facebook page shortly before the ceasefire expired, the envoy urged “all parties to agree to its extension for at least another renewable 72 hours”.

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.

But shortly after the appeal, coalition warplanes on Sunday attacked Shia rebel positions in the capital Sana’a, military officials and rebel media said.

The rebel-controlled sabanews.net website counted nine airstrikes on the capital at dawn on Sunday. The raids hit positions in Ma’rib, east of the rebel-held capital, and the southwestern province of Taiz, officials said.

“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 said.

“We respect the UN envoy’s call for an extension, but in effect, there was no truce” due to 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 border 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 of Najran.

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