The Syrian government lacks the will to conduct negotiations on political change in the country, opposition delegates said on the fifth day of UN-brokered peace talks in Geneva.
"At the moment there is no partner on the other side who is willing to engage," leading opposition negotiator Bassma Kodmani told dpa.
"We're waiting for a change of attitude as a result of Russian pressure. This has not come yet," she said, referring to the military and political alliance between the governments in Moscow and Damascus.
The UN broker at the talks, Staffan de Mistura, had said Thursday that the government side would hopefully also present its proposal on political transition in the war-torn country, with the opposition side having already delivered theirs.
However, President Bashar al-Assad's chief negotiator Bashar al-Jaafari said Friday that his side was still focussed on a set of basic principles for the talks that it had submitted earlier this week.
"We believe that the adoption of these principles, that we have called fundamental elements, will lead to a serious intra-Syrian dialogue to help build the future of our country," al-Jaafari said after his latest meeting with de Mistura.
According to the UN envoy, the government and opposition do not yet share any common ground on a political transition process.
While al-Assad has given no indication that he is willing to relinquish power, the opposition says he cannot rule any longer.
Kodmani said al-Assad should leave before planned elections, which the UN Security Council has said should take place within 18 months.
"There will be no free elections as long as he is in charge of everything," she said.
De Mistura has mainly been shuttling between regime and exiled opposition delegations since he restarted the talks this week, but he has also consulted with opposition figures who have remained in Syria and are seen as closer to the government.
Ahmad Alkoussa, a delegate of the so-called internal opposition, rejected the idea that the president would have to step down before a national vote.
"Syrian President Bashar al-Assad is an elected president from the people, and only the people can decide on it," he told reporters in Geneva.
The current round of Geneva talks was made possible by a ceasefire, brokered by the United States and Russia, which has been largely holding.
However, the truce agreement does not extend to the extremist militia Islamic State.
At least 16 people including eight children were killed Friday when planes raided Islamic State's de-facto capital al-Raqqa in northern Syria, a monitoring group said.
The Britain-based Syrian Observatory for Human Rights did not say if the air raids in several areas of al-Raqqa were carried out by Russian, government or US-led coalition planes.
Meanwhile Amaaq news agency, which has links to Islamic State, reported that the extremist group killed five Russian soldiers in fighting near the ancient city of Palmyra.
Syrian regime forces backed by Russian planes launched an attack on Palmyra last week after the UNESCO World Heritage city was seized by Islamic State last May.
Russian President Vladimir Putin on Monday ordered the Russian military to withdraw the majority of its forces from Syria.
But Moscow asserted Friday that its planes will continue bombing UN-designated terrorist organizations Islamic State and al-Nusra Front in Syria.