As embattled Yemeni President Ali Abdullah Saleh struggles to crush al-Qaida in the center and south of Yemen as well as anti-regime protests led by a defecting army general, landlocked Houthi rebels in the north are driving to open an arms route to the Red Sea.

If they succeed, their advance could heighten tensions between Iran and Saudi Arabia who are locked in an escalating confrontation for control of the Persian Gulf region.

There have been suggestions the resurgent campaign by the rebels, members of Yemen's minority Zaidi Shiites, has been aided by Iran.

There's been no independent confirmation of that, although Tehran was reported to have provided weapons to the Houthis in their last major battle with Sanaa in 2009-10.

Iran's Islamic Revolutionary Guard Corps Special Forces reportedly helped the Houthis fight forces deployed against them by neighboring Saudi Arabia, which feared the insurgency would trigger unrest in their border provinces.

Saudi Arabia, a Sunni monarchy that's guardian to Islam's holiest shrines, and Shiite Iran, its main rival in the Persian Gulf region, are engaged in a deepening conflict by proxies that shows every sign of getting worse.

The Houthis, who have been in rebellion against the Sanaa government since 2004, have gained tactical control of territory in northern Saada province, their main base, and neighboring al-Jaw province, both of which border Saudi Arabia.

The Yemen Observer has reported they've been pushing westward across northern Yemen in recent weeks in a clear attempt to open up a supply route to the Red Sea while Saleh's regime and the Saudis are preoccupied further south.

"They will face challenges as they expand … but Sanaa's distractions might allow them to gain access to the coast, which could facilitate better access to foreign weapons suppliers and would push Saudi Arabia to respond," observed the U.S. global security consultancy Stratfor.

The Houthis' main strategic objective appears to be Midi, a small port with access to the Red Sea through which to funnel weapons, and the nearby coastal town of Salif.

One of the rebels' main weaknesses has been a shortage of arms, which for some time has limited their operational capabilities.

Midi's harbor cannot accommodate large vessels. But its importance became evident in November 2009 when the Saudi navy blockaded Yemen's northern Red Sea coast through the Iranians were supposedly moving supplies to the rebels.

No doubt the Saudi navy's western fleet, which has headquarters at Jeddah, will seek to seal the port again. That could raise tensions and a possible confrontation at sea.

Iran has been sending warships into the Red Sea of late, partly to provoke the Saudis in their current confrontation, and might be inclined to respond if the Saudis blockade Midi.

"Riyadh fears that any success by the Houthis in Yemen would inspire the group's fellow Zaidis across the border," Stratfor noted. "If the Houthis can secure a path to these ports, the Saudis likely would intervene."

The Saudis' 2009 intervention, Operation Scorched Earth, began only after the Houthis had seized control of areas that Riyadh deemed dangerously close to the mountainous and highly porous border with its provinces of Najran and Jizan.

Stratfor cited reports that in the 2009 fighting, the IRGC trained Houthi insurgents to make improvised explosive devices, like those used by Iranian proxies in Iraq.

They reportedly shipped supplies to the rebels through the port of Assab in southern Eritrea on the western shore of the Red Sea, which the IRGC also uses to ship weapons to the Palestinian radicals of Hamas in the Gaza Strip.

The Iranian shipments were then funneled through Salif and Huth on Yemen's northern coast bound for the Houthi stronghold in Saada.

Another reported route was from Assab to the Gulf of Aden off the southern tip of the Arabian Peninsula, then by sea to Shaqra in southern Yemen and north via Marib province to Saada.

With the U.S. military withdrawal from Iraq creating a power vacuum Iran is driving to fill and which Saudi Arabia seems unable to prevent, a revived Houthi rebellion against the beleaguered Saleh in Sanaa would weaken a key -- if not entirely trustworthy -- ally at a critical time in the region.

"Saudi Arabia has an interest in keeping potential Iranian influence in Yemen away from the southern Saudi border," Stratfor noted.