The Sochi congress on Syria kicked off on Tuesday after a two-hour delay sparked by disputes between United Nations envoy to Syria Staffan de Mistura, the Turkish delegation and Russia. Sources told Agence France Presse that the differences emerged over de Mistura’s demand to form a constitutional reform committee that he would chair. He also submitted a list of possible candidates for the committee, but it was rejected by Russia. Turkey meanwhile expressed its reservations over the Syrian regime’s dispatch to Sochi of a figure it deems to be a terrorist. Russian Foreign Minister Sergei Lavrov telephoned his Turkish counterpart Mevlut Cavusoglu in order to resolve the dispute. Regime-backer Moscow has invited 1,600 delegates to the meeting in the Black Sea resort of Sochi as part of efforts to reach a political solution to the Syrian conflict. Syrias main opposition group and Kurdish authorities are boycotting the event, while on Tuesday separate rebel representatives were at Sochi airport but refused to come to the congress before Russia met demands. "There have been some problems with an armed opposition group arriving from Turkey, which said its participation depended on additional requirements," Artem Kozhin of the Russian foreign ministry said in comments reported by the TASS news agency. A rebel source told AFP that Russia had promised to change or remove the symbol of the congress, which features only the Syrian regime flag. But the airport, the road to the conference center and the congress hall itself were still decorated with banners and billboards bearing the logo when the rebels arrived on Monday night, leading to hours of ongoing negotiations. Turkish Foreign Ministry officials said the Syrian delegation decided not to attend the Sochi congress in protest of the pictures and logos. Instead, the officials said Turkey would represent that group in Sochi. The Syrian opposition later denied the Turkish claims. The main aim of the Sochi talks is to establish a committee to create a post-war constitution for Syria with United Nations backing, according to a draft statement seen by AFP. Moscow said Syrian society would be fully represented at the meeting -- the first of its kind held in Russia -- but almost all confirmed delegates are from either Bashar al-Assads Baath Party, allied movements or the regimes "tolerated opposition". The Syrian Negotiation Commission (SNC), the countrys main opposition group, said following two days of UN-led talks in Vienna last week it would not attend the Sochi congress. The SNC accused Assad and his Russian backers of continuing to rely on military might and showing no willingness to enter into honest negotiations. The start of the conference itself was also not without incident. Speaking at the opening session, Lavrov said that "all circumstances are ripe for peace in Syria." Soon after, some Syrian delegates stood up and heckled the minister, accusing Moscow of killing civilians in Syria with its air strikes, a Reuters witness said. Syrian official Ghassan al-Qalaa said: "I call you upon in the name of millions of Syrian to have mercy upon our country." The incident was also broadcast live on Russian state TV where two security guards were shown approaching one man in the audience indicating that he should sit down and be quiet. Other delegates at the conference in the Russian Black Sea resort of Sochi stood up at the same time and shouted their support for Russia, the Reuters witness said. Lavrov told the delegates to let him finish speaking, saying they would have their own say later on Tuesday.