No one knows precisely how many Iraqi volunteers are crossing the border to fight in Syria, but it is clear there are enough to keep a steady stream of corpses returning home for burial.
The funeral this month of Dhia Mutashar Gatie al-Issawi in Basra is one of many. The young bricklayer, 26, died earlier this month in Damascus while fighting for the Syrian government.
How he got to Syria remains a closely guarded secret. But there was nothing secretive about the funeral, which brought out scores of proud mourners.
His brother, Mustafa Mutashar, says he died defending Shi'ite tombs in Syria from desecration.
"At the time, he said that he was going to seek martyrdom defending [the shrine of] Saida Zainab, and our pride increased when we learned of his martyrdom, since we are Shi'ite," Mutashar tells RFE/RL's Radio Free Iraq. "The funeral procession stretched from Shalamcha to here. It was attended by a representative of the Said's office [of Iraqi Shi'ite cleric Muqtada al-Sadr]."
The shrine of Saida Zainab commemorates the daughter of Shi'ite Islam's first imam, Ali. It is one of several key shrines in Syria regarded as particularly sacred by both Syria's government -- whose Alawi leadership follows a mystical offshoot of Shi'ism -- and mainstream Shi'a across the region.
But if no one at the funeral will say how Mutashar reached Syria, the presence of a representative of the "Said" -- the honorific title of radical Shi'ite cleric Muqtada al-Sadr -- offers a possible explanation.
All Roads Lead To Damascus
Sadr's Al-Mahdi Army is one of several Shi'ite militias widely believed to be sending fighters to Syria. Some of the others are the Iraqi Hizballah Brigades and the Asaeb Ahlul-Haq.
Farther north, in Iraq's central Al-Anbar Province, a bastion of Sunnism, funerals for martyrs in Syria also occur regularly. Only these ceremonies are for men who have died fighting on the opposite side of the conflict: in support of the majority Sunni Syrian opposition.
Sheikh Muhammad al-Hayis is an official with the Sons of Iraq, or Iraqi Awakening. At the height of Iraq's sectarian unrest in 2007, when Al-Qaeda sought to spark a civil war between Sunni and Shi'ite militias, his movement helped crush Al-Qaeda in the Sunni heartland and restore stability.
Sheikh Muhammad al-Hayis, a Sunni tribal chief, in Anbar
Hayis says Sunni radical groups such as Al-Qaeda in Iraq are sending fighters to support their Syrian counterparts, such as the Al-Nusra Front. The bodies of the dead fighters are smuggled back to Iraq concealed among frozen goods traded across the border and returned to their relatives. Then, he says, they are buried quietly for fear of attracting the attention of Iraq's Shi'ite-dominated government, which is against regime change in Syria.
"We have information about incursions into Syria from Iraq, especially from Al-Anbar, Mosul, and other governorates, to fight the Syrian people and their government, aiming at the destruction of the Syrian people and the Syrian government," Hayis says. "That is what we have seen -- large numbers of killers and criminals who are accustomed to killing people and beheading them."
'Weak Government Measures'
The fact that Iraqi volunteers are fighting on opposite sides of Syria's war raises fears for Iraq's own fragile sectarian peace.
Ibrahim al-Sumaydai, an Iraqi political analyst in Baghdad, says many of the groups sending fighters to the war in Syria see it as a Sunni-Shi'ite showdown. He warns that unless the Iraqi government stops the flow of fighters, their battles in Syria could spill back into Iraq.
"There is a struggle between the Sunni and Shi'ite crescents -- two sides or two camps, one consisting of the Gulf states and Turkey in opposition to Iran," Sumaydai says. "I feel that this situation will cause a rift within Iraq. The [Iraqi] fighters involved there -- for one reason or another -- are Sunnis and Shi'ites and they will eventually be fighting each other [face to face]. This may have a negative impact on the Iraqi scene and on Iraqi society. That is, the looming danger of the matter, which has so far been met by very weak government measures."
Since the height of Iraq's sectarian unrest, Baghdad has been able to enlist most of the militias into a national reconciliation effort, and many have been converted into political parties.
But the effort has yet to achieve its key goal of disarming the militiamen themselves. Until it does, there is no certainty that the militias will not one day return to the streets, this time to settle their battlefield scores from Syria.
Iraq remains a highly volatile place, with the number of bombings and assassinations targeting both Sunnis and Shi'a increasing over the past month. This week alone, some 90 people have been killed and scores more wounded in a wave of violence that began with government forces raiding a Sunni protest camp in northern Iraq in April.
Written by Charles Recknagel in Prague based on reporting by Radio Free Iraq's Samira Ali Mandee. Radio Free Iraq correspondents Abdelkareem Al-Amiri from Basra, Ahmed Al-Bashir from Anbar, and Ahmed Al-Zubaidi from Baghdad also contributed to the report