The Saudi-led coalition killed eight civilians in two separate air strikes on rebel-controlled areas of northern Yemen on Thursday, a government official said.

Warplanes from the coalition, which supports forces loyal to President Abedrabbo Mansour Hadi, hit "by mistake" a vehicle at Razah in Saada province, killing five civilians, said the official.

Another air strike killed three civilians travelling in a vehicle in Shadeh, a village also located in Saada, said the same source.

Saada province is a stronghold of the Iran-backed Shiite Huthi rebels who overran the capital Sanaa in September 2014 before going on to seize other provinces.

Human rights groups accuse the coalition, which has stepped up its strikes against rebel positions especially in northern Yemen, of a string of such attacks that have killed civilians.

On September 22, at least 20 civilians died in coalition air strikes on rebel-held Hodeida, in western Yemen, in what a government official said was a possible "error".

The conflict between Yemen's government and the Huthi rebels escalated in March last year with the intervention of the Arab coalition in support of Hadi's government.

More than 6,600 people are estimated to have been killed since then, most of them civilians, according to the United Nations.