RIYADH (Reuters) - Mortars and rockets fired at Saudi Arabian towns and villages have killed 375 civilians, including 63 children, since the start of the Saudi-led military campaign in Yemen in late March, Riyadh said on Monday.

Brigadier General Ahmed Asseri, spokesman for the Saudi-led coalition in Yemen, told Reuters that the Houthi militia and army forces loyal to former president Ali Abdullah Saleh had fired more than 40,000 projectiles across the border since the war began.

“Now our rules of engagement are: you are close to the border, you are killed,” he said.

In a measure of how fierce the fighting on the frontier continues to be, nearly 130 mortars and 15 missiles were fired by the Houthis and Saleh’s forces at Saudi border positions on Monday alone, Asseri said in an interview in Riyadh.

Riyadh has been sharply criticized for civilian casualties in coalition air strikes and on Sunday announced it was improving its targeting mechanisms and would form a committee to investigate claims it had hit non-military targets.

Around 6,000 people, about half of them civilians, have been killed in fighting and coalition air strikes in Yemen since the war began, according to the United Nations. The civilians killed in Saudi Arabia included both Saudis and expatriates, Asseri said.

Riyadh’s campaign was launched to stop the Houthis, who are allied to Riyadh’s main regional foe Iran, from gaining complete control over Yemen after they seized the capital in 2014 and drove President Abd-Rabbu Mansour Hadi into exile.

Yemeni forces backed by the coalition pushed the Houthis from the main southern port city of Aden in June and from the northeastern town of Marib in September, but have since made little territorial progress.

STATIC WAR

Fighting has continued since September in Yemen’s third-largest city of Taiz. The Houthis and Saleh’s forces hold the surrounding mountains and coalition-backed forces inside the city and to the south have been unable to break their siege.

Along the Saudi-Yemen border, the constant attacks by the Houthis and Saleh’s forces have forced Riyadh to evacuate a dozen villages and displace over 7,000 people from frontier districts, closing over 500 schools, Asseri said.

He said the coalition had taken “hundreds” of Yemeni prisoners in fighting along the border.

Asseri acknowledged that the forces were locked in what he described as a “static war”, but said the coalition was now fighting to control the mountainous Nahm region, which controls access to the capital Sanaa 70 km (40 miles) to the southwest.

Humanitarian organizations have criticized the coalition for its naval blockade of Yemen, aimed at stopping the Houthis from gaining military supplies, but which they say has pushed the country to the brink of famine.

Asseri said the coalition was now allowing more ships to dock both at Aden and the Houthi-controlled Red Sea port of Hodeida. The coalition conducts random inspections of cargo, he said, but added that it believes some weapons are smuggled through.