MAPUTO -- Stunned by a last-minute ballot boycott decreed by the former Renamo rebel movement, anxious Mozambicans voted Thursday in multi-party elections supposed to seal peace after 16 years of civil war.


Renamo's decision, announced by an angry Afonso Dhlakama, the movement's leader who was also contesting the presidency against incumbent Joaquim Chissano, sent tremors through southern Africa where leaders feared a possible return of the civil war that ravaged Mozambique until two years ago.


Long queues of first-time voters, many women with babies strapped to their backs, formed before voting booths opened at 7 A.M. Witnesses said Renamo monitors, who had not heard of their party's boycott, turned up at some stations.


Dhlakama, alleging widespread fraud, demanded new elections. But he said he would not return to the war in which hundreds of thousands were killed and millions turned into refugees.


"We have made this decision because we have proof that there will be massive fraud in this election. It is not an election, it is a picnic ... we want new elections," Dhlakama told reporters at his sea-front house in the Indian Ocean port of Beira.


The Renamo leader told reporters he would fly to the capital Maputo later in the day, but was not willing to be persuaded to change his mind.


Dhlakama's boycott sent diplomats and UN monitors into a frenzy of activity, spurred by the example of how elections failed to end war in another former Portuguese colony, Angola, where rebels returned to the battlefield after losing a UN-monitored election.


A Portuguese special envoy in Beira and diplomats from Britain and Zimbabwe met the Renamo leader after the boycott was announced early in the morning.


UN special envoy Aldo Ajello, who has overseen the deployment of 7,000 UN peacekeepers and 2,400 international observers, was holding crisis meetings in Maputo.


The president of the independent National Electoral Commission, Brazao Mazula, said in a message on state radio that Renamo's fraud allegations had no foundation.


"None of the questions involve problems that could put in question the elections' validity," he said, urging the country's 6.4 million registered voters to cast their ballots.


Prime Minister Mario Machungo, standing halfway along a queue of about 1,000 voters, said the Renamo decision was "regrettable."


State radio reported a big voter turnout under sunny skies around the huge but impoverished country. Results are not expected until around mid-November.


Twelve presidential candidates and 14 parties or coalitions are taking part in the elections but the polls are effectively a battle between Chissano and his ruling Frelimo party, and Dhlakama and his Renamo movement.