The Mozambican government and Renamo, the rebel movement that turned opposition, failed on Wednesday to agree on a ceasefire after six rounds of talks.
The government refused to consider Renamo's demand for parity in the army and in the security forces, and vowed to stage the October 15 elections without Renamo's participation if necessary.
Government delegation head Jose Pacheco called Renamo's demands “an authentic coup d'etat”.
Renamo representative Saimone Macuiana said its demands needed to be met for it to disarm.
“We will do everything so that the two sides can find a solution,” said Bishop Dinis Sengulane, one of the observers to the dialogue between the government and Renamo.
Renamo on Tuesday staged an ambush against a military convoy one day before the negotiators met. Pacheco said the ambush occurred in the central province of Sofala, where the two sides have been fighting since last year.
He did not give casualty figures but reports said two soldiers were killed and four injured.
Pacheco said the violence was typical of Renamo, but the opposition party accused the government of attacking its forces in the area.
Renamo is the former rebel group that signed a peace deal with the ruling Frelimo party in 1992, ending the long and bloody civil war that followed the departure of colonial power Portugal from the southern African country.
Renamo is the largest opposition party in Parliament with 51 of 250 seats.
It has nevertheless killed dozens of people in highway attacks, demanding a more equitable distribution of the country's wealth and a change to electoral laws. - Sapa-dpa