SANAA: Yemen’s warring factions Sunday braced for a key battle in a central province, where victory could allow pro-government forces to move rapidly north into the heartland of the country’s Shiite rebels.

Security officials from both sides said the focus was now on Marib, an oil-rich province that supplies the rebel-held capital of Sanaa with electricity and fuel, after months of combat and airstrikes that have killed some 2,000 civilians, according to the U.N.

An airstrike by warplanes from a Saudi-led coalition, which said it targeted a bomb-making factory, killed 36 civilians working at a bottling plant in the northern Yemeni province of Al-Hajjah Sunday, residents said.

In another air raid on the capital Sanaa, residents said four civilians were killed when a bomb hit their house near a military base in the south of the city. “The process of recovering the bodies is finished now. The corpses of 36 workers, many of them burnt or in pieces, were pulled out after an airstrike hit the plant this morning,” resident Issa Ahmed told Reuters by phone from the site in Al-Hajjah.

Coalition spokesman Brig. Gen. Ahmed Asseri denied the strike had hit a civilian target, saying it was a location used by the Houthis to make improvised explosive devices and to train African migrants whom they had forced to take up arms.“We got very accurate information about this position and attacked it. It is not a bottling factory,” he said.

Pro-government forces have recently tightened their grip on the province’s capital, also called Marib, while the Shiite rebels, known as Houthis, have consolidated their positions on its outskirts, digging trenches and laying mines in nearby Jawf, security officials from both sides and witnesses said.

If pro-government forces manage to push the rebels out of Marib, they could potentially advance rapidly across Jawf, a flat, desert province bordering Saudi Arabia that is also a gateway to Saada, the rebels’ northern stronghold, where Saudi planes have been dropping flyers urging people to support the “legitimate” government of internationally recognized president Abed Rabbou Mansour Hadi.

Yemen’s conflict pits the Houthis and allied units of the splintered army against forces loyal to Hadi as well as southern separatists, local militias and Islamist militants. Hadi and his government are in exile in Saudi Arabia.

In their foothold in Marib, the pro-government forces were joined earlier this week by hundreds of Yemeni fighters, fresh from military training in neighboring Saudi Arabia, which has been leading the Arab coalition launching airstrikes against the Houthis since March, pro-government security officials said.

Saudi forces have made repeated small incursions across the border with Yemen in response to attacks since the start of airstrikes against Houthi forces March 26, the Saudi-led coalition said Sunday. “Sometimes you have to move and not be static on your defensive line. You move, find where the attack comes from, find the target. It happens from time to time but is not significant,” spokesman Asseri said.