By Andrew Cawthorne
CARACAS (Reuters) - Venezuela's government on Friday blasted the United States for linking an activist's murder to upcoming legislative elections and said it would sue an opposition leader who blamed the ruling Socialist Party.
The killing of Luis Diaz, a leader of opposition Democratic Action party in central Guarico state, has rocked Venezuela days before the vote for a new National Assembly, which the Socialists risk losing for the first time in 16 years.
Diaz was shot dead at a campaign rally on Wednesday.
In the emotional aftermath, Henry Ramos, national head of Democratic Action, and Lilian Tintori, wife of jailed opposition leader Leopoldo Lopez and a witness to the shooting, blamed the ruling party.
But President Nicolas Maduro said initial investigations pointed to a gang dispute. Officials accused the opposition of exploiting the case to discredit the Socialists before the Dec. 6 election.
"Trying to link a murder between criminal gangs with Venezuela's electoral process shows desperation and bad faith," Foreign Minister Delcy Rodriguez said of a U.S. statement linking it to other aggression against opposition candidates.
Democratic Action is part of an opposition coalition that polls show has a strong chance of winning the legislature, which would be a heavy blow to the ruling "Chavismo" movement, named for late former leader Hugo Chavez.
Opposition leaders have for several weeks been denouncing hostility against their candidates, including several incidents of shooting in the air during marches.
But the head of the government's election campaign, Jorge Rodriguez, said Diaz had been part of a gang linked to extortion, murders and kidnapping, and named an alleged rival as his presumed killer.
Rodriguez said he would bring a lawsuit against Democratic Action head Ramos for defamation of the Socialist Party.
"From Jan. 5 onward, I am going to investigate you all for the multiple crimes you have committed," Ramos retorted, referring to the date the new National Assembly starts.
The killing brought widespread international condemnation.
The United Nations urged Venezuela on Friday to provide better safety for political opponents and rights defenders.
Underlining a cooling of relations with Maduro, regional heavyweight Brazil also weighed in, expressing "dismay" at Diaz's death.
"The Brazilian government hopes the Venezuelan government will act to deter any acts of violence or intimidation that might call into question the credibility of the electoral process and the legitimacy of the voting results," a Foreign Affairs Ministry statement said.
(Additional reporting by Tom Miles in Geneva, Alonson Soto in Sao Paulo; Editing by Girish Gupta, G Crosse and Bill Trott)