BEIRUT (AP) -- In a reflection of how intertwined the Syria and Iraq conflicts have become, thousands of Shiite Iraqi militiamen helping President Bashar Assad crush the Sunni-led uprising against him are returning home, putting a strain on the overstretched Syrian military as it struggles to retain territory recaptured in recent months from rebels.
The borders between the two countries are being largely ignored, with fighters from the Islamic State of Iraq and the Levant said to be crossing freely from one side to the other, transporting weapons, equipment and cash in a development that has potential to shift the balance of power in a largely stalemated battle.
The seizure of large chunks of Iraq by militants does offer Assad a messaging victory: he has long insisted that the uprising against him is the work of foreign-inspired Islamic extremists, suggesting that the West needs to work with him to check the influence of jihadis, and that the radicals, not the divided and weaker pro-Western moderate rebels, are the real alternative to his rule.
The violent actions and speedy successes of the same group in Iraq, against a government the West does essentially support, seem to align with his argument. And he can relish the fact that the U.S. is weighing airstrikes against Sunni militants in Iraq -- and possibly Syria -- while shying away from any military action against his government for the past three years.
But the developments also threaten to upset what has recently been an upward trend by Assad's forces in the three-year-old Syrian conflict.
The Syrian government is heavily reliant on foreign fighters to bolster its ranks and help quell the largely Sunni insurgency engulfing the country. They include thousands of Shiite Hezbollah fighters, Iranian Revolutionary Guard advisers and Iraqi militiamen who left their homes and headed to Syria to defend what they see as an attack on the Shiite regional axis comprised of Iran, Assad, Hezbollah in Lebanon and Prime Minister Nouri al-Maliki's government in Iraq.
That axis is now under mounting pressure. The militants of the Islamic State of Iraq and the Levant are carving out an ever-expanding fiefdom along the Iraqi-Syrian border. Earlier this month, they seized Iraq's city of Mosul -- and they have vowed to march on to the Iraqi capital Baghdad as well. In the past few days, the militants seized two strategically located towns along the Euphrates River, including the Qaim border crossing with Syria -- advancing their efforts to etch out a large region straddling the two conflict-ridden countries.
"The developments in Iraq are a double-edged sword for Assad," said Randa Slim, a director at the Washington-based Middle East Institute. "On one hand, these developments help Assad's narrative to his constituents and to the West that his fight is with terrorists and not against democrats." On the other hand, she said, the Islamic State's rapid and successful incursion into Iraq undermines Assad's claim that he is able to defeat them.
In the most immediate outcome, thousands of Iraqi Shiite militiamen fighting in Syria are heading back home to defend against the Sunni blitz, leaving behind gaping holes in areas under their control.
In interviews conducted by The Associated Press with returning Shiite fighters in Baghdad, many said they were responding to a call to arms issued in recent days by Iraq's Shiite spiritual leader Ali al-Sistani. Others said they considered Iraq to be the mother battle.
"Yes, we took part in the fighting in Syria. But now the priority is Iraq," said Jassem al-Jazaeri, a senior official in Iraq's Hezbollah Brigades, which is believed to be funded and trained by Iran's Revolutionary Guard.
Most of the Shiite Iraqi fighters in Syria -- believed by some estimates to number between 20,000 and 30,000 -- have been battling rebels in suburbs of the Syrian capital and particularly in the vicinity of Sayida Zeinab, home to a major Shiite shrine by the same name.
Syrian opposition activists say Syrian rebels are already exploiting the vacuum left by the Iraqis to mount attacks. A number of Hezbollah fighters were killed in an attack on the town of Rankous in the Qalamoun region last week. The town fell to government and Hezbollah forces two months ago.
Firas Abi Ali, head of Middle East and North Africa Analysis, IHS Country Risk, said in a recent analysis that the Syrian government will compensate for any redeployment of Iraqi fighters using manpower drawn mainly from Hezbollah.
"However, the Iraqi fighters' departure would probably temporarily reduce the ability of the Syrian government to mount new offensives and place it on the strategic defensive," he said.