Al-Jumaili came from the Iraqi city of Fallujah, which was a hotbed of the Sunni insurgency and one of the first areas where militants stood their ground against American troops after the 2003 U.S.-led invasion of Iraq.
One of the journalist's relatives, Khalid al-Jumaili, told The Associated Press that his cousin traveled to Syria "to show the world the misery of the Syrian civilians and he was not part of the struggle between the rebels and the government."
He said his cousin was 38 years old and had a daughter and two sons.
"The killers should know that they did not only kill a human being, they destroyed a whole family," Khalid al-Jumaili said by telephone from Fallujah.
Al-Jumaili worked in the past for Al-Jazeera TV and Reuters. It was not immediately clear who he was working for on his last trip.
Abdurrahman said the shooting took place somewhere between the towns of Saraqib and Maaret Musreen. He said the gunmen were foreign fighters believed to be members of the al-Qaida-linked Islamic State in Iraq and the Levant.
"They stopped him at the checkpoint and opened fire immediately without asking any questions," he said.
North of Damascus, meanwhile, opposition activists accused the government of using poison gas in an attack on a rebel-held area of the contested town of Nabek.
Amer al-Qalamouni, an activist, said shells used in the bombardment produced a white, yellowish smoke and a strange odor. He said seven people were exhibiting symptoms consistent with gas attacks, such as foaming at the mouth.
The government swiftly denied the reports, saying in a statement carried by the state news agency that the claims were "categorically false and baseless."
The opposition has accused the government of using chemical weapons on several occasions over the course of Syria's nearly three-year-old conflict.
An chemical strike on rebel-held suburbs of Damascus in August killed hundreds of people. Each side blamed the other for the attack.
After the U.S. threatened to carry out punitive missile strikes against the government, Assad agreed to give up his chemical arsenal, and international experts are currently overseeing the program's destruction as part of a deal brokered by the U.S. and Russia.
In another development, the Observatory said that 12 nuns taken by rebels from the predominantly Christian town of Maaloula north of Damascus earlier this week are still in the rebel-held town of Yabroud.
On Thursday, Syria's Greek Orthodox Patriarch, John Yazigi, pleaded for the release of the nuns, saying that he cancelled a trip to the Gulf and will head to Syria on Friday to follow up on the case.
"We call upon the international community, all governments to work on getting them out safely," Yazigi told reporters in the Balamand Monastery in northern Lebanon. "What we want today is good and tangible acts, not talks."
On Wednesday, Pope Francis called for prayers for the nuns, who were reportedly taken by force from their convent in Syria by rebels. Religious officials in the region have said the women were abducted, but a Syrian opposition activist has said they were merely removed for their own safety.
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Associated Press writers Sameer N. Yacoub in Baghdad, Zeina Karam and Ryan Lucas in Beirut contributed to this report.
