Residents inspect damaged ground after a shell fell in the rebel held town of Jarjanaz, southern Idlib countryside, Syria March 5, 2016. REUTERS/Khalil Ashawi

The U.S.-Russia-brokered ceasefire in Syria may be the last chance to end violence in the war-torn nation, opposition groups said in a joint statement after a meeting at the Russian center for Syrian reconciliation, media reports said Wednesday. The news comes as a spokeswoman for the United Nations envoy in Syria said Tuesday that "substantive" peace talks with both Syrian government officials and opposition representatives will be held within days.

Ahead of the peace talks, leaders of several Syrian opposition groups as well as public and religious figures voiced support for the ongoing peace conference in Geneva aimed at ending Syria's conflict, which erupted in March 2011 as a popular uprising against Syrian President Bashar Assad's authoritarian rule, and turned into an all-out civil war that led to militant groups such as the Islamic State group and the Nusra Front gaining control over large parts of the country.

On Tuesday, opposition groups called on all Syrian patriots to participate in the U.N.-backed reconciliation process, RT News reported, adding that the groups also pledged to take part in the future work on a new Syrian constitution.

The new constitution “will ensure that Syria exists as a prosperous, strong, democratic, independent and secular country that respects the rights of every citizen regardless of his ethnic or religious status,” the opposition statement said, according to reports.

Although the talks will officially resume on March 9, some participants will reach Geneva not later than March 14, U.N. Syria envoy Staffan de Mistura’s spokeswoman Jessy Chahine told a regular U.N. briefing, according to Reuters.

Earlier this month, the U.N. reportedly said that the Geneva talks, originally slated to kick off on March 7, were delayed by two days due to "logistical and technical reasons and also for the ceasefire to better settle down.”

The opposition forces, along with their backer Saudi Arabia, had initially expressed reluctance to join the peace talks, insisting that Assad must step down. The Syrian opposition protested against violations by Assad’s forces of an internationally-brokered ceasefire in place since Feb. 27.

Last week, Assad reaffirmed his commitment to the truce saying it offered a “glimmer of hope” for Syria, adding that "terrorists have breached the deal from the first day. We as the Syrian Army are refraining from responding in order to give a chance to sustain the agreement and that is what we can do. But in the end there are limits and it all depends on the other side.”

About 4.6 million people have reportedly fled Syria since the civil war began five years ago. Another 13.5 million are said to be in need of humanitarian assistance inside the country as tensions escalate in the region.

Russia entered the conflict at the end of September 2015 when it began airstrikes, but faced criticism from Western officials who claimed that the Kremlin targeted opposition groups to help longtime ally Assad remain in power.