Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.

Secretary of State John Kerry on Sunday urged Syria's government and the war-torn country's opposition groups to "seize the opportunity" to participate in U.N.-backed peace talks.

“This morning in light of what is at stake in these talks, I appeal to both sides to make the most of this moment, to seize the opportunity for serious negotiations, to negotiate in good faith with the goal of making concrete measurable progress in the days immediately ahead," Kerry said in Washington.

The talks started Friday in Geneva — without the main opposition bloc known as the Higher Negotiations Committee, who said they won't join peace discussions until the Syrian government and Russian lift sieges on rebel-held area.

The talks experienced another setback Sunday when the head of the Syrian government delegation said blasts in Damascus that killed at least 60 people served as proof of the link between the opposition groups and terrorists.

Kerry said Sunday that there was no military solution to the civil war in Syria, and that diplomatic negotiations were the only hope for the country's suffering people.

"The bloodshed will drag on without negotiations," Kerry said. "That will ensure an increased number of terrorists."

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

Kerry encouraged the opposition groups and government — whom have been asked by U.N. mediators to meet in separate "proximity talks" — to "make the most of this moment."

"We call on the parties in Geneva to take the first urgent step and not to miss that chance this moment presents," Kerry said.

Humanitarian aid to Syrians must be allowed immediately. “Surrender or starve” tactics are directly contrary to the law of war. — John Kerry (@JohnKerry) January 31, 2016

He said some 13.5 million Syrians — nearly half of them children — are living in government-besieged towns and cities, and only 1 percent of those people received desperately needed food aid in 2015.

“We must not forget what the Syrian people will always remember, Assad and his allies have from the very beginning, been by far the primary source of killing, torture and deprivation in this war,” Kerry said.

Related: Madaya Siege: Aid Workers Entering Starving Town Find Shocking Scenes

The goal of the talks would be to declare a ceasefire between the feuding parties and set up the framework to hold elections within 18 months so that "Syrians can determine the future of Syria," Kerry said.

A spokesman for the Syrian opposition High Negotiations Committee (HNC), Salem Al-Meslet, said the HNC was in Geneva with the goals of stopping the sieges, putting an end to bombardments and releasing political prisoners and detainees. He made the remarks before meeting with U.N. Special Envoy to Syria Staffan de Mistura Sunday.

After the meetings, the discussions were described as "very positive," especially with regards to the humanitarian situation.

"Today's meeting was very positive with Mr. de Mistura," he told reporters. "Things are encouraging and positive concerning humanitarian issues. There will be another meeting tomorrow."

The opposition said earlier in the day it would not enter political negotiations with President Bashar al-Assad's government until there were concrete measures in place that would alleviate the humanitarian situation on the ground.