"There are merely delegates in Geneva who have the government's backing and who share its views," al-Assad said.
Ibrahim Jebbawi, a member of the Syrian opposition delegation in Geneva, called al-Assad remarks "baseless."
"There is a delegation representing the Syrian government and was chosen by him [al-Assad]. He is still manoeuvring," Jebbawi told dpa. 
Yehia Aridi, a member of the Syrian opposition group, the High Negotiating Committee, lashed out al-Assad. 
"Detachment from reality is still reigning," Aridi told dpa, referring to al-Assad's comment.
The Geneva negotiations started in earnest on Thursday following a ceremonial opening on the previous day, with 150 delegates representing the Syrian government, the opposition and civil society in equal parts.
In the interview, al-Assad also played down the legitimacy of the opposition delegates, saying they represent Turkey and the United States. "A few represent the terrorists," he added.
Foreign ministers making up the so-called Small Group on Syria welcomed the establishment of the constitutional talks in a statement released in Berlin on Friday.
The ministers from the United States, France, Britain, Germany, Saudi Arabia, Egypt and Jordan described the move as "a long-awaited positive step that requires serious engagement and commitment in order to succeed."
"It can complement implementation of other dimensions of Security Council Resolution 2254 [calling for a ceasefire and political settlement in Syria], including the meaningful involvement of all Syrians, especially women, in the political process.
"We support efforts to create a safe and neutral environment that enables Syria to hold free and fair elections, under UN supervision."
The ministers called for an immediate and genuine ceasefire, adding that there could be no military solution to the conflict that erupted in 2011, has claimed thousands of lives and displaced half the population.
On Thursday in Geneva during the first working session of the UN-brokered talks between the warring sides the debate became heated over the Syrian army's role.
Syrian opposition sources said that a dispute erupted when a member of the government lauded the army and its "martyrs." Opposition delegates immediately protested.
Ankara and Washington have been supporting forces that are fighting al-Assad's army in Syria's eight-year civil war. In contrast, Russia is giving military support to the Syrian president.
On Thursday, UN Secretary General Antonio Guterres expressed hope that the Geneva talks could lead to a broader peace process to end Syria's devastating war.
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