A US journalist who went missing in war-torn Syria is believed held by a military intelligence unit at a detention center near Damascus, a spokesman for his family said Friday. James Foley, a 39-year-old freelancer who has filed reports for GlobalPost, Agence France-Presse and other outlets, has not been heard from for 162 days, since he was seized by gunmen in a town near the Turkish border. Foley's family and employers insist he was working in Syria as an objective, professional reporter, and have called for his release. Syrian officials have never publicly acknowledged having any news of his whereabouts. On Friday, his family and GlobalPost held an event in Boston on World Press Freedom Day to press Syrian President Bashar al-Assad's government for news. The co-founder and CEO of the online news network, Phil Balboni, said his company had hired the international security firm Kroll to investigate. "With a high degree of confidence, we now believe that Jim was most likely abducted by a pro-regime militia group, commonly referred to as the Shabiha, and subsequently turned over to Syrian government forces," Balboni said. "We have obtained multiple independent reports from very credible confidential sources who have both indirect and direct access that confirm our assessment that Jim is now being held by the Syrian government." Balboni said the detention facility where Foley is reportedly being held is near the Syrian capital Damascus in an area still controlled by forces loyal to Assad's regime, which is battling an armed revolt. "We further believe that this facility is under the control of the Syrian Air Force Intelligence service," he said, promising that GlobalPost would continue to press through private and diplomatic channels for Foley's release. Balboni said that GlobalPost knows the name and location of the detention center, and believes that other international journalists are also being held there, but said he could not go into details for security reasons. Foley, an experienced reporter who had worked in several conflict zones, was seized by armed men in the northern Syrian province of Idlib on November 22, according to witnesses, and has not been heard from since. Several international and Syrian journalists are reported as missing in Syria, which descended into civil war after March 2011, when a revolt erupted against Assad's rule. Some have later been released. In Paris, AFP chairman and chief executive Emmanuel Hoog issued a fresh call for Foley's release. "This new information on James Foley is encouraging and gives us hope that we will see him freed as soon as possible," Hoog said in a statement. "It is long past time for James to be sent home to his family and loved ones. On this World Press Freedom Day, I am launching a new appeal to all those who could help make this happen, and in particular, the Syrian authorities." A report by human rights watchdog Amnesty International released on Friday to mark World Press Freedom Day estimated that 36 journalists have been killed covering the conflict, in what the group called "targeted attacks." The report lays the blame for much of the violence towards reporters on the regime, including on the feared Air Force Intelligence unit, but also accuses Islamist rebel groups such as Jabhat al-Nusra of some of the killings. Foley's mother, Diane Foley, said the news that her son may be in regime custody has given the family renewed hope that he might be freed. "I'm thankful that they presume that Jim's alive, and that they've zeroed in," she told AFP. "It's very daunting to think he's in Damascus, because there's so much going on in Damascus. It's a very dangerous place." "But we are very hopeful... that the Syrian government will recognize Jim is an objective, innocent journalist, who cares for the Syrian people and was there to report their story," she said. Foley had previously been captured by troops fighting for Libyan strongman Moamer Kadhafi while he was covering the fighting there in March 2011. He was released after several weeks in custody. His family maintain a campaign website (freejamesfoley.org), a Facebook site (facebook.com/freejamesfoley) and Twitter account @freejamesfoley. The campaign's Boston event was supported by GlobalPost and Northwestern University's Medill School of Journalism. Tributes were paid to Foley's work, and a panel of journalists discussed their experiences as former captives.