As negotiations intended to end Syria's three-year-old war concluded the second day of this week's session, both sides had no advances to report.
Brahimi, a veteran diplomat charged with running the internationally sponsored talks, said he planned to report to UN Secretary General Ban Ki-moon and the Security Council within the next few weeks.
"The beginning of this week is as laborious as it was in the first week. We are not making much progress," he told a news conference at United Nations headquarters.
Syrian Deputy Foreign Minister Faisal Muqdad said Tuesday was a "lost day" while opposition spokesman Louay Safi said "no progress" had been made.
In an attempt to address the main questions confronting the rival delegations, Brahimi had proposed that they discuss ending the violence on Tuesday and the formation of a transitional governing body on Wednesday, delegates say.
But the two issues have caused deep rifts and delayed negotiations, which started last month with little result and resumed this week.
A main issue is denouncing terrorism and acting against radical groups which are fighting at the side of Syrian opposition.
The opposition refuses to include the issue as one of the most powerful groups fighting for them is al-Qaeda’s al-Nusra Front.
Instead the opposition insists on removing Syrian President Bashar Assad, an issue which has been announced by the government as a redline, because it puts the country in more danger than it has been suffering.
Muqdad said no agenda had been agreed for the talks.
"Today was another lost day because the representatives of the (opposition) Coalition insisted that there is no terrorism in Syria," he said.
So far, the only tangible result of the talks process has been an agreement to allow aid into the Old City of Homs.
Syria sank into war in March 2011 when pro-reform protests turned into a massive insurgency following the intervention of Western and regional states.
The unrest, which took in terrorist groups from across Europe, the Middle East and North Africa, has transpired as one of the bloodiest conflicts in recent history.
SHI/SHI