Riyadh is currently hosting talks aimed at unifying Syrian opposition parties' positions ahead of the next round of Syrian peace talks with international mediators, expected to take place at the beginning of 2016.
"Participants underlined that Assad and his associates should leave power at the beginning of the transitional period," the statement reads, according to the source.
The document also states that the opposition conference participants are ready to start talks with representatives of the Syrian government, the source said.
During the first round of Vienna talks, the international mediators worked out a nine-point plan on ending the four-year Syrian civil war, including a definition of national unity, the need to defeat of extremist groups and to provide assistance to refugees.
During the second round of the talks, mediators agreed to uphold the 2012 Geneva communique on finding a political solution to the Syrian conflict and set a six-month timeframe for Syria to form an interim unity government, while stipulating that elections in Syria should be held within 18 months.
