Houthi rebels have gained ground east of the Yemeni capital Sanaa, in what the defence minister acknowledged as a "tactical withdrawal" by government loyalists.

Renewed fighting, which entered its ninth day on Saturday, allowed the rebels to retake loyalist positions, loyalist commanders told AFP news agency.

"Some of these positions had been under government control for three years," one of the commanders said on condition of anonymity.

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Defence Minister General Mohammed Ali al-Maqdishi implicitly recognised the rebels' advance in the Nihm area in comments published by the official Saba news agency.

Al-Maqdishi spoke of a "tactical withdrawal from some positions" during a meeting on Friday with loyalist commanders.

The loyalist forces would be redeployed to open a new front against the rebels, al-Maqdishi said, claiming "the battle to liberate Sanaa has become inevitable".

The rebel advance came despite extensive air support for government forces from its allies in a Saudi-led coalition.

Coalition planes "attacked Houthi positions more than 30 times in the last three days to reduce the pressure on the loyalists," one commander said.

The government accused the rebels of killing 116 people in a January 18 missile attack on a loyalist military camp in Marib province, east of Nihm.

The Houthis neither claimed nor denied they were behind that attack, which came a day after fighting between the two sides resumed, breaking months of relative calm.

In a report published on Friday, the International Crisis Group said the "Houthis appeared to be making the biggest gains on the battlefield".

The think-tank warned that if the renewed fighting spread, it would represent "a devastating blow to current efforts to end the war".