RIYADH: Bombs fired from territory held by Yemen's Houthi militia into a Saudi Arabian border town killed five people on Wednesday, Saudi officials said, as the rebel group stepped up an apparent retaliation for weeks of air strikes by a Saudi-led coalition.

Mortar shells and rockets fired into the town of Najran and a village in Jizan province on Tuesday claimed the first Saudi civilian casualties of the conflict, and prompted coalition jets to hit targets in northern Yemeni towns.

The coalition is considering all options, including ground operations, to prevent more such attacks, its spokesman Brigadier General Ahmed Asseri said in a televised interview on al-Arabiya channel. Asseri has said since the start of the campaign that land operations were a possibility.

One shell landed near security forces patrolling near the prison in Najran, killing an officer, while another killed four Saudi civilians, including two in a car and two others at a car repair shop, the city's Civil Defence told official media.

More than 30 coalition raids and artillery fire responding to Tuesday's shelling of Najran and other border areas killed 43 civilians in Yemen's Saada province, Houthi and other local sources said on Wednesday.

Reuters could not verify the figures.

Saudi Arabia and its nine Arab coalition partners began air strikes against the Houthis and army units loyal to a former president on March 26 aimed at restoring the government of President Abd-Rabbu Mansour Hadi, who has fled to Riyadh.

However, although the strikes have destroyed weapons held by the Houthis and Saleh, they have not weakened their grip on territory they control and have contributed to a worsening humanitarian situation across Yemen.