Saudi Arabia imposed a naval blockade on the Red Sea coast of northern Yemen to stem the flow of weapons and fighters to Shiite rebels along its border, a Saudi government adviser and media reports said Tuesday.

Iran, the dominant Shiite power in the Middle East, warned neighboring countries not to interfere in Yemen's internal affairs in a clear reference to predominantly Sunni Saudi Arabia. Yemen and the Saudis have accused Iran of sending money and weapons to the rebels to fight government forces. Iran denies the charge.

"We seriously recommend the regional countries and especially the neighboring countries not interfere in the internal issues of Yemen and instead try to restore stability in Yemen," Iranian Foreign Minister Manochehr Mottaki said Tuesday.

Saudi Arabia launched an air and ground offensive against the Yemeni rebels last week. The fighting has raised concerns of another proxy war in the Middle East between Iran and rival Saudi Arabia, a key U.S. ally.

Yemen has been embroiled in a sporadic, five-year conflict with Shiite rebels in northern Saada province along the border with Saudi Arabia. The Shiites accuse authorities of neglecting their needs and of allying with hard-line Sunni fundamentalists.

Fighting has intensified since August, displacing tens of thousands of people and limited their access to humanitarian aid.

Yemen's weak central government of Yemen, which has little control outside the capital San'a, is fighting on multiple fronts including the northern rebels and a separatist movement in the south. But the most worrisome is a lingering threat from al-Qaida militants.

The Saudi blockade was the latest escalation of fighting in the impoverished country at the southern tip of the Arabian peninsula.

After some border clashes between the rebels and Saudi forces last week, the Saudis responded with rare cross-border military action. They launched several days of airstrikes against the rebels, which continued on Tuesday according to the rebels.

An adviser to the Saudi government told The Associated Press on Tuesday the kingdom's warships had been ordered to search any suspected ship sailing near the Yemeni coast for weapons or fighters destined to aid the rebels. He spoke on condition of anonymity because he was not authorized to speak to the media. Saudi-owned Al-Arabiya satellite television also reported the blockade.

Also Tuesday, Prince Khaled bin Sultan, the Saudi assistant defense minister, said the rebels must "withdraw dozens of kilometers" inside Yemen before the Saudi military would halt its assault.

Saudi defense expert Anwar Ashki said the Saudi army has tightened its control of the border area but has no plans to invade Yemen. Continued...