UN-Arab League envoy Lakhdar Brahimi, who arrived in Damascus Monday, believes President Bashar al-Assad could contribute to the transition to a "new" Syria, but not as the country's leader.

Brahimi, who was in Syria on the latest leg of a regional tour to rally support for peace talks, spoke about Assad in an interview in Paris with the Jeune Afrique website published Monday.

"Many of those around (Assad) believe his candidacy (for a new presidential term in 2014) is a fact. He considers this an absolute right... He thinks above all of completing his mandate," the veteran Algerian diplomat said.

However, "what history teaches us is that after a crisis like this there is no going back. President Assad could therefore usefully contribute to the transition from the Syria of before, that of his father (the late president Hafez al-Assad) and himself, to what I call the new Republic of Syria."

Brahimi said the US-Russian accord to dismantle Syria's chemical arsenal had transformed Assad from a "pariah" into a "partner" and convinced his supporters even more of his ability to prevail.

Brahimi also faces an uphill battle in convincing the fractured opposition to attend the Geneva talks, after 19 Islamist rebel groups warned that anyone taking part in the talks would be considered a traitor.

"This conference is the beginning of a process. We hope that the opposition will manage to agree on a credible and representative delegation," Brahimi said.

"We should not delude ourselves: the entire world will not be present. But as the process continues, it should include as much of the world as possible."

Brahimi, a veteran international troubleshooter, said he feared that if a settlement could not be reached Syria may become a failed state like Somalia, which has not had a functioning government for two decades.

"The real threat in Syria is not the partition of the country. The real danger is a sort of "Somalisation," but even more deep and lasting than what we have seen in Somalia."