Nov. 11 (Bloomberg) -- Fighting in northern Yemen between government troops and Shiite Muslim rebels has forced thousands of civilians to flee in recent days, the United Nations said as it called for secure corridors to deliver aid.

“We again appeal for the protection of civilians and secure and unhindered access for humanitarian workers,” Andrej Mahecic, a spokesman for the UN High Commissioner for Refugees, told reporters in Geneva yesterday.

The UN says about 175,000 people have been affected by the conflict in the northwestern province of Saada, which broke out in 2004 and escalated in August. The World Food Programme said aid routes are unreliable and this week said their may be “widespread suffering” if it’s unable to re-stock supplies.

Yemen’s government accuses the rebels of trying to reinstall the rule of Shiite imams who were toppled by a republican revolution in northern Yemen in 1962. The Houthi rebels, named after their leader Abdul-Malik al-Houthi, say they want a greater role for their Zaydi version of Shiite Islam and are revolting against corruption in the government and its alliance with the U.S.

The fighting has spread across Yemen’s 1,500-kilometer (930- mile) border with Saudi Arabia, which began an air bombing campaign against the rebels earlier this month after a Saudi border guard was killed. The rebels said in a statement yesterday they have taken control of the Qatabir district on the border with Saudi Arabia and seized military positions.

Border Crossing

The UNHCR said Saudi authorities have made assurances the Alp border crossing is stable, allowing aid agencies to continue delivering supplies across the frontier into northern Yemen.

About 2,000 people, mostly elderly, single mothers and children, have fled Saada in recent days, Mahecic told reporters, according to the agency’s Web site. They are now staying at the Al Mazrak refugee camp in Hajja to the southwest, which hosts 8,700 displaced people, he added.

Iran yesterday warned neighboring countries not to interfere in the internal affairs of Yemen as a top Saudi defense official said air strikes would continue until the rebels have retreated tens of kilometers from the border.

Yemen accuses Shiite-led Iran, the main regional rival to the Sunni Muslim kingdom of Saudi Arabia, of arming the insurgents.

Proxy War

The conflict wasn’t sectarian historically, as the Houthis, estimated at between 6,000 and 7,000 armed men, had formed close links with local Sunnis, and Yemen’s President Ali Abdullah Saleh is himself a Zaydi, according to the Washington Institute for Near East Policy.

Nevertheless, it has the makings of a proxy war between Iran and Saudi Arabia, Simon Henderson, director of the institute’s Gulf and Energy Policy Program, said in a report e-mailed today.

“The crisis in Yemen could have serious consequences for Gulf security,” Henderson said. More than 3 million barrels of oil a day pass through the Bab al-Mandeb Strait at the south end of the Red Sea en route to Europe, he said.

The Yemeni navy said it seized an Iranian-crewed ship in the Red Sea loaded with weapons near a stronghold of the rebels on Oct. 26. Iran described the allegation as a “media fabrication.”

To contact the reporter on this story: Ed Johnson in Sydney at ejohnson28@bloomberg.net.

Last Updated: November 10, 2009 20:08 EST