* Saudi forces try to keep Yemen rebels away from border
* 10 km deep "kill zone" no place for civilians
* Saudi navy patrols off northern Yemen - Saudi govt adviser
By Alistair Lyon, Special Correspondent BEIRUT, Nov 12 (Reuters) - Saudi Arabia is using air power and artillery to enforce a 10 km (six mile) deep buffer zone inside Yemen to keep Yemeni rebels away from its southwestern border, a Saudi government adviser said on Thursday.
Saudi officials said heavy guns had pounded insurgent positions across the border on Thursday to create what Saudi media have called a "kill zone". The defence ministry spokesman in Riyadh could not immediately be reached for comment.
The adviser, who asked not to be named, said the zone would be no place for civilians while the conflict raged. Any Yemenis caught crossing into Saudi Arabia would be interrogated to make sure no fighters were among them and then placed in camps.
Saudi Arabia, the world’s biggest oil exporter, launched an offensive last week after rebels seized some Saudi territory on the mountainous border which they said the Saudis had been allowing Yemeni troops to use to attack their positions.
Prince Khaled bin Sultan bin Abdul-Aziz, Saudi assistant minister for defence and aviation, said on Tuesday the Zaidi Shi’ite rebels, known as Houthis after their leaders’ clan, had been driven from Saudi territory and that the Saudi offensive would continue unless they retreated well away from the border.
The Saudis are on particularly high alert for any security threat as Muslim pilgrims flock to the kingdom for the annual haj pilgrimage to Mecca which begins on November 25.
The Saudi government adviser said no Saudi troops were fighting inside Yemen where the terrain was in any case too mountainous to deploy tanks and artillery effectively.
"The orders are not to go physically into Yemeni territory," he said. "We don’t want to get bogged down there or inflame any local sensitivities, if there are any, against us."
He said Saudi ships had begun patrolling the coast off northern Yemen with air support three days ago to prevent any weapons or other supplies reaching the insurgents by sea, in what would be a rare unilateral operation by the Saudi navy.
Yemen said last month it had seized a ship carrying weapons destined for the rebels and detained its five Iranian crew — a report dismissed by Iranian state media as a fabrication.
The Saudi government adviser said there was little evidence Iran was directly aiding the Houthis, even if it wanted to. Iran denies any involvement and has offered to mediate in the war.
Fighting between Yemeni troops and Houthis, who say Yemen’s Zaidi Shi’ite minority suffers discrimination and neglect, has flared on and off since 2004 in the northern province of Saada.
In August President Ali Abdullah Saleh ordered the army to launch Operation Scorched Earth to try to crush the revolt, touching off the heaviest round of conflict so far. Aid groups say it has forced up to 150,000 civilians to flee their homes.
The United Nations refugee agency said last week it was looking into whether Saudi air strikes had affected 3,500 to 4,500 displaced people gathered near the border.
Saudi Arabia and its ally, the United States, fear al Qaeda militants are exploiting instability in Yemen, an impoverished country also grappling with separatist unrest in the south, to establish a stronger base for operations in the region.
The Saudi government adviser said the Houthis were also under pressure from Yemeni forces. Those captured by the Saudis were only lightly armed, poorly fed and "in no state to fight".
The rebels said on Tuesday they had captured additional territory near the 1,500 km (930 mile) Saudi-Yemeni border. (Additional reporting by Souhail Karam in Riyadh; editing by Samia Nakhoul)