Makdissi fled to Lebanon and was brought to the United States with the help of U.S. intelligence officials, the British newspaper The Guardian reported.
Recent statements from the Syrian government said he was on a "three-month sabbatical" and others claimed he was kidnapped by Lebanon's Hezbollah group and returned to the Syrian regime, the al-Arabiya news channel reported.
Hezbollah's television station in Damascus, Lebanon, said Dec. 3 Makdissi was fired for making statements inconsistent with official government positions.
United Nations-Arab League special envoy Lakhdar Brahimi has made no headway in talks with Syrin President Bashar Assad but will stay until Sunday, an official said.
Hasan Abdul-Azim, head of the opposition National Coordinating Body, told reporters in Damascus after meeting with Brahimi that the special envoy plans to stay in Syria until Sunday, China's official Xinhua News Agency reported.
Syrian opposition groups say they have documented 18 incidents in which the regime has used chemical weapons. Quoting opposition elements in Syria it did not name, Israel Radio reported Tuesday chemical weapons used in the Damascus, Idlib, Homs and Hama areas used a kind of gas not known to be in the regime's chemical weapons supply. The report said no international body has been able to certify the claims.
Meanwhile, the Syrian Network for Human Rights said its daily count of casualties listed 156 people killed across Syria Tuesday, including 10 children and eight women. The violence continued to be heaviest in the Damascus area, where 55 fatalities were reported.
The group's numbers were unverified.
Brahimi, who arrived in Damascus Sunday, said talks had made no progress, the Los Angeles Times reported.
"The situation in Syria is still worrying and we hope that all parties would adopt a solution that would meet the aspirations of the Syrian people," the Times quoted him saying.
The official Syrian Arab News Agency reported Assad was pleased with the Brahimi visit and described the meeting as "constructive and cordial." Assad said he is willing "to ensure the success of any efforts in the interest of the Syrian people which saves the country's sovereignty and independence."
A Damascus diplomat whose name was not reported said Assad is "totally aware" he must leave Syria, and was "looking for a way out," The New York Times reported. "Powerful people in the upper circle of the ruling elite in Damascus are feeling that an exit must be found," the paper quoted the diplomat saying.
The Local Coordination Committee of Syria said it had its own peace demands and would reject any initiative whereby Syrians would be "forced to choose between accepting unfair compromises or the continuation of the regime's crimes against them," CNN quoted the committee saying Tuesday.
The committee called on Assad and his officials to step down immediately and said they would refuse any requests for immunity, CNN said.
An estimated 40,000 people have been killed since the outbreak of violence in March 2011.