JIZAN: Shiite rebels said on Sunday they shot down a Yemeni combat aircraft on the Saudi border nearly three months into a widening war between the insurgents and government forces.

Jet fighters from Saudi Arabia, which entered the fray on Tuesday after the rebels seized two of its villages and killed a border guard, stepped up bombing raids against rebel positions.

The kingdom said three of its soldiers have been killed and another four have gone missing since the fighting erupted on the rugged border, also claiming the lives of an unknown number of Yemenis.

The rebels said however that besides capturing several Saudi soldiers, they had also downed a Yemeni government aircraft.

"Our anti-aircraft batteries have shot down a military aircraft which was bombing the village of Razeh" close to the Saudi border, rebel spokesman Mohammad Abdessalam told AFP.

A military source in Sanaa acknowledged a Russian Sukhoi bomber had crashed because of "mechanical problems."

It is the third combat aircraft the Zaidi rebels claim to have downed since the launch of the government offensive against them on August 11. Yemen says all of the incidents were due to mechanical reasons.

The Zaidi rebels, who were forced towards the mountainous border with Saudi Arabia by Yemeni troops, told AFP "the Saudis are continuing their air and land shelling of Yemen territory near the border with Saudi Arabia."

An defiant statement on their website said earlier that "with Allah's help, the Saudi tyrannical advance into Yemen's territory has been defeated.

"A number of its troops have been captured and several military vehicles and supplies been seized."

Saudi Deputy Defence Minister Prince Khaled bin Sultan denied late on Saturday any of his soldiers had been taken.

But "there were five missing and one came back. They are missing and not prisoners" of the rebels, the prince said according to the official SPA news agency.

Speaking near the front in Jizan province, Prince Khaled also said Saudi forces had recaptured all territory seized by the rebels earlier in the week.

"The operation resulted in the death of three members of the security forces and the wounding of 15, most of whom have left the hospital."

If the rebel claim is true, it would add a new complexity to Riyadh's first overt entry into the Yemen domestic conflict.

On Wednesday Riyadh unleashed F-15 and Tornado jets against rebel positions around the massive Jebel al-Dukhan mountain, which soars 2,000 metres (6,600 feet) out of the coastal plain on the border in southern Jizan province.

Ground troops and heavy long-range artillery lined the sides of the main road to the frontier town of al-Khubah at the foot of the mountain on Saturday as soldiers patrolled fields and inspected vehicles for rebel fighters.

Saudis said some rebels had infiltrated into the country disguised as women in all-black abaya shrouds.

While officials from both countries said the Saudi attacks took place only inside Saudi Arabia, the rebels and a Saudi official admitted jets attacked rebels well inside their bastion of Yemen's Saada province adjacent Jizan.

The rebels accused Riyadh of permitting Yemeni troops to use Saudi territory to attack their flank.

The intensity of the Saudi attack has surprised some analysts who note Riyadh's close support of Yemen President Ali Abdullah Saleh.

Prince Khaled called the Saudi response "a rebuke to intruders who had infiltrated the borders of the kingdom."

According to government and medical doctors in the region, seven Saudis have been killed in the fighting, including four women whose border home had been shelled, and three security personnel.

Doctors at the regional hospital said they had treated 126 people injured in the fighting, the largest part on Friday when a dozens of soldiers arrived with gunshot or shrapnel wounds.

Casualties on the Yemeni rebel side are unknown. The Saudi-controlled newspaper Asharq al-Awsat reported that 155 rebels had been captured by Saudi forces in the fighting.