"Basically, when I felt I could not help my people any more I had to move on," Danny Al-Baaj, the first Syrian diplomat in Switzerland to abandon the Assad’s regime.
"When I was involved in any negotiations (on Syria) my concern was to protect the country not the government," he added.
Al-Baaj's move comes a week after Syria's Prime Minister Riyad Hijab defected along with other top officials and military commanders.
Baaj said he took his decision a long time ago and had been in contact with the Syrian opposition group the Democratic Forum, which is based in Paris.
"I met Syria's charge d’affaires (in Geneva) and I told him I had made my decision that I was going to the opposition... He said it was my choice and he wished me luck," Baaj added.
Baaj described the Democratic Forum as one of the main opposition groups. The group is headed by Michel Kilo, a long-time opponent of the regime.
The development comes ahead of the release on Wednesday of an official UNHRC independent commission of inquiry report into Syria.
Baaj said he "hoped" the Geneva-based body would make progress toward consensus on the situation in Syria despite many countries letting their own agendas interfere with finding a solution.
"At the last session the HRC was very close to reaching consensus ... I hope different countries put aside their agendas to help the Syrian people," he said.
Baaj also stressed his opposition to outside military intervention in the conflict but supported the role of the UN’s Supervision Mission in Syria (UNSMIS), calling it "a good thing."
"I hope it stays there. It’s very important to document abuses by both sides," he said.
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