SANAA, Yemen, Dec. 1 (UPI) -- Saudi Arabia's escalating war against rebels in neighboring Yemen elevates what had been a local insurrection against Sanaa into a conflict with regional dimensions that could ignite bigger fires in a part of the world that is already staring into the abyss.
The monthlong fighting, which capped a five-year tribal rebellion in the mountains of northern Yemen, exacerbates regional rivalries and deepens the potentially dangerous 1,200-year-old schism between Sunni Muslims and their Shiite cousins.
There is an ironic echo in all of this, harking back to earlier rivalries.
The Saudis are now fighting tribes they supported in Yemen's civil war during the 1960s when the 1,000-year-old imamate to which these same royalist tribes bore allegiance was overthrown by republicans.
The republicans were supported by Egyptian President Gamal Abdel Nasser, then the icon of Arab nationalism. Now, in the personage of President Ali Abdullah Saleh, they rule in Sanaa and are being backed by Riyadh.
At the center of this complex web of regional rivalries lies the longtime contest between Saudi Arabia and Iran over who will be the paramount power in the strategic, oil-rich Gulf.
Even before the 1979 Islamic revolution of Ayatollah Ruhollah Khomeini toppled the U.S.-backed Shah of Iran, the two Gulf neighbors were vying for supremacy.
The Iranian revolution only enflamed the mutual hostility, with the Saudis bankrolling Saddam Hussein's Iraq in the 1980-88 Gulf war against the ancient Persian foe to block its westward encroachment into the Arab world.
Riyadh claims that Tehran is supporting, arming and training the Yemeni rebels, who are Shiites like the overwhelming majority of Iranians. But, like Saleh's government in Sanaa, the Saudis have yet to produce concrete proof of this.
The grand mufti of Sunni-dominated and Sunni-ruled Saudi Arabia, Sheik Abdulaziz al-Sheik, has accused Iran of "collusion in sin and aggression" and demanded that the Islamic Republic's Sunni minority be protected.
Gen. Hassan Firouzabadi, the chief of staff of Iran's military, accused the Saudis of committing "state terrorism" by aiding Saleh's beleaguered government and poorly performing military against the Shiite tribesmen.
The Saudis' military intervention in Yemen, the first such action since the 1991 Gulf war by a kingdom that has long pursued more diplomatic strategies, could well intensify the simmering proxy conflicts Riyadh and Tehran are waging in Lebanon, the Palestinian territories and Iraq.
For Saudi Arabia, the most immediate objective is to ensure that Saleh's regime in Sanaa, corrupt and inept though it is, does not collapse, because that could transform Yemen into a springboard for a resurgent al-Qaida to launch a new offensive to topple the Saudi monarchy -- and possibly spread further afield.
Iran is feeling increasingly isolated after the internal turmoil triggered by President Mahmoud Ahmadinejad's disputed re-election in June and the U.S.-led drive to make it abandon its nuclear program.
It is no mood to be pilloried by its old monarchist rival Saudi Arabia or its allies. This hostility could well be carried over into Tehran's growing intransigence in its diplomatic dealings with the United States on the combustible nuclear issue.
"Those who pour oil on the fire must know they will not be spared from the smoke that billows," Iranian Foreign Minister Manouchehr Mottaki warned.
If the U.S. initiative to solve the nuclear issue founders, the prospect increases that Israel, jittery about the challenge to its regional nuclear monopoly and growing international criticism about alleged war crimes, could launch the pre-emptive strike it has threatened for so long against Iran.
The Saudi-Iranian faceoff is heightened by Riyadh's fears of Iranian and Shiite expansion following the emergence of a Shiite-ruled Iraq. The deadlock in efforts to secure an Arab-Israeli peace, after a decade-and-a-half of futile negotiations, only makes things more fraught.
But at the root of all this is the religious schism between the Sunnis, Islam's mainstream sect, and the breakaway Shiites that dates from Islam's early days in the 7th century over who should have succeeded the Prophet Mohammed.
The prospect of a direct confrontation between Saudi Arabia and Iran over Yemen, fueled of course by the covert activities of both sides in Lebanon, Iraq and the Palestinian territories, will be heightened if the fighting in Yemen gets worse and drags in others.
And right now there's little sign it's about to diminish.