(CNN) The day before Syrian peace talks are due to start in Geneva, Switzerland, the leader of a coalition of Syrian opposition groups tells CNN that Bashar al-Assad has no interest in reaching a political solution to the nearly 6-year-old civil war.
"I know Bashar al-Assad. I used to be his prime minister before I defected. And I know about his barbarism," Riyad Hijab told CNN's Christiane Amanpour in an exclusive interview Thursday. He spoke with Amanpour from Riyadh, the capital of Saudi Arabia, whose government backs his group.
Hijab was prime minister for two months in Assad's government in 2012 before his defection.
"He believes in military solutions only -- he does not want a political process. Neither does Russia. All they want is a military resolution. That's why they come to such peace talks, in order to make them fail."
Russia became involved in the Syrian conflict in the fall to support its longtime ally, Assad. Moscow at the time said its goal was to combat ISIS, but the United States says that Russia has mainly been bombing the Syrian opposition and that civilians have been caught in the crossfire.
As with so much about the Syrian conflict, the U.N.-brokered peace talks are shrouded in confusion.
Originally meant to start Monday, the negotiations were delayed until Friday over "posturing," as U.N. special envoy Staffan de Mistura put it, and a lack of clarity over who would represent the opposition.
It's unclear whether Hijab's group will attend the so-called proximity talks, which would -- as the name suggests -- have the Syrian regime and opposition negotiate without engaging in face-to-face discussions. De Mistura plans to shuttle from room to room, meeting individually with the warring factions.
"We are completely serious in such peace talks, and we are willing to go at any moment," Hijab said.
But before engaging in negotiations, he told Amanpour, his group must see implementation of humanitarian provisions in a U.N. Security Council resolution passed in December, the first such agreement in the Syrian war.
That document mandated that all sides "immediately allow humanitarian agencies rapid, safe and unhindered access," allow delivery of basic needs like food and medicine, release "arbitrarily detained persons" and "immediately cease any attacks against civilians."
Hijab said his coalition has sent a letter to U.N. Secretary-General Ban Ki-moon requesting an update on implementing the resolution.
"We have no prior conditions -- all we are asking for is to, for everyone to abide by their commitments," he said.
Michael Contet, a spokesman for de Mistura, told CNN that the U.N. envoy replied to Hijab on Wednesday night.
"Our response indicated that the most efficient way to obtain the implementation of the rightful request for confidence-building measures and ceasefires is for (the opposition High Negotiations Committee) to come to Geneva and discuss their implementation with the U.N., and through us, with all interested parties."
In a follow-up after Amanpour's interview, Mohammed Alaa Ghanem, who works with Hijab, said the opposition coalition had just received a phone call from U.N. Deputy Secretary-General Jan Eliasson, urging the group once again to attend.
U.N spokesman Farhan Haq confirmed the call, saying the two men discussed "participation in Geneva."
"We would like to go," Ghanem relayed Hijab as having told Eliasson, "but please work with us on this so that our people are satisfied."