The Movement for Democratic Change party said an arson attack on the home of an election candidate in eastern Zimbabwe killed the politician's 12-year-old son. The attack was one of 120 incidents of violence recorded so far this year, said the third ranked MDC official, Finance Minister Tendai Biti.
The candidate's house has suffered nine attacks surrounding previous elections and the last violent and disputed elections in 2008. The child's burial is to be on Thursday.
Biti said his party was "enraged at the increase in politically motived violence throughout the country" that he blamed on a faction of President Robert Mugabe's party.
Biti accused Mugabe's ZANU PF party of attempting to once again instill fear in the electorate.
"ZANU PF intends to harvest fear in the 2013 elections," he said.
He also alleged that Mugabe's security services have crafted a strategy of intimidation, arrests and possible assassination attempts against leaders of the former opposition in a shaky coalition government with Mugabe.
Voters go to the polls March 16 in a referendum on a new constitution, followed by parliamentary and presidential elections slated around July to end the coalition brokered by regional mediators after the troubled 2008 vote.
No arrests have been made in the death of the 12-year-old. Party officials said it took seven hours for police to reach the scene of the fire in the Headlands district, 140 kilometers (90 miles) east of Harare, on Saturday.
Mugabe's party, blamed along with loyalist police and military for much of the political violence surrounding elections over the last decade, has denied the involvement of its supporters in the fire at Headlands, a stronghold of a staunch veteran Mugabe ally,Didymus Mutasa.
The United States embassy in Harare immediately called for urgent and impartial investigations into the alleged arson attack.
"Respect for the law and apolitical policing are essential for creating conditions for credible and non-violent Zimbabwe elections this year," it said in a statement.
Both Mugabe and Tsvangirai have repeatedly called for violence-free elections.
Human rights monitors of an independent group, HealZimbabwe Trust,said authorities on Tuesdayattempted to stop mourners and sympathizers gathering at the scene of the fire.
Tsvangirai party activist and aspiring lawmaker Shepherd Maisiri, the father of the dead child, said communities were fast losing confidence in the calls for peace by political leaders, according to the trust's information bulletin on Tuesday.
The trust quoted Maisiri telling its monitors:" I am told I must trust Robert Mugabe that elections are going to be peaceful. Well, this is proving false.My son is dead before we even get to the referendum. What more will happen as we approach highly contested elections?"
The Zimbabwe Election Support Network also reported Tuesday its observers noted the re-emergence of feared pro-Mugabe youth militia groups in several parts of the country.
It reported "instability and political tension" across the nation.
"Observers continue to report the presence of intolerance and a generalized lack of freedom of association and expression," the group said.