SANAA (Reuters) - At least 21 civilians were killed in two separate air strikes by the Saudi-led coalition in northern Yemen on Saturday, residents said on Sunday, as fighting intensified in the country before the Muslim Eid al-Adha feast.

At least 15 civilians were killed when war planes struck workers drilling for water in the Beit Saadan area of the Arhab district north of Sanaa, and 20 people were wounded, residents in the area, controlled by Iran-allied Houthi forces, said.

They said Saudi-led coalition warplanes bombed the site and killed four workers, and then conducted a second bomb run when residents of the village rushed to the scene, killing at least 11 more and wounding 20.

"We heard three explosions, and people rushed out to help the people working on the drills. Then the planes came back and launched five strikes causing this number of dead and wounded," Saif Saleh, a witness, told Reuters by telephone.

A spokesman for the Saudi-led coalition, General Ahmed al-Asseri, said "all operations in the area were targeting Houthi positions and members."

The coalition, which has been fighting to roll back gains made by the Houthi group since 2014 and restore ousted President Abd-Rabbu Mansour Hadi to power, says it does not target civilians.

U.N.-sponsored talks to try to end the fighting collapsed in failure last month and the Houthi movement and allied forces loyal to former president Ali Abdullah Saleh resumed shelling into neighboring Saudi Arabia.

Saturday's attacks were the latest in a series of strikes that have hit schools, hospitals, markets and private homes.

Local media put the number of dead and wounded at the water-drilling site at around 100 and published pictures of burned bodies and mangled equipment. Videos showed workers collecting mutilated bodies and carrying them away in blankets.

In a second attack, residents reported an air strike hit the home of Sheikh Maqbool al-Harmali, a local tribal chief in Hairan district of Hajjah province, killing six civilians.

The United Nations says more than 10,000 people have been killed in the fighting, many of them civilians.

In an Eid message, Hadi said: "We will not allow Iran to turn Yemen into an arena for the blackmail of neighbors."

Iran denies any interference in Arab states.

In south-eastern Abyan province, a suicide bomber killed seven police conscripts and wounded 15 on Sunday when he drove a vehicle laden with explosives into a police compound in Hadi's hometown, a local official said. No one claimed responsibility for the attack in al-Wadea district.

(Reporting by Mohammed Ghobari, writing by Sami Aboudi and Katie Paul; Editing by William Maclean, Ralph Boulton)