International negotiators have failed to agree on whether to invite Iran to peace talks over the Syrian conflict, the UN-Arab League envoy on Syria said, according to BBC News.

Lakhdar Brahimi said the U.S. remained unconvinced that Iran's participation "would be the right thing to do".

He said some 26 nations had been asked to join the conference, which is due to be held in Switzerland in January.

The U.S., UN and Russia have been struggling for months to get the talks, known as Geneva II, off the ground.

The conference aims to ensure the delivery of humanitarian aid, end the fighting and outline a political transition for Syria.