Santo Domingo, Dominican Republic (CNN) -- Dominican lawmaker Danilo Medina declared victory in the nation's presidential elections in a series of Twitter posts Monday, but his closest competitor has yet to concede.
"Today, thanks to the sovereign decision of the Dominican people, I am the president of all Dominicans," Medina wrote.
He led with 51% of the vote, with 99% of votes counted in the election authority's preliminary tally of Sunday's election results.
His closest competitor, former President Hipolito Mejia, had not conceded as of Monday night. The preliminary tally gave him 47% of votes. A candidate must garner 50% of the vote plus 1 to avoid a second round of voting.
In an interview with CNN en Español on Monday, Medina vowed to address drug trafficking, education and incomes in a country where more than one-third of the population lives in poverty.
He said he would work toward creating conditions such that young people have opportunities to pursue other than crime.
"I want to build a middle-class society. That is my main goal -- to have a population that is able to go shopping, to have the capacity to consume," he said.
The election is a rematch of the nation's 2000 presidential contest, where Mejia defeated Medina. Since the end of Mejia's term in 2004, the presidency has been held by Leonel Fernandez, of the centrist Dominican Liberation Party, the same party that Medina belongs to.
Mejia represents the left-leaning Dominican Revolutionary Party.
Some see the candidates as similar in some respects, but passions nonetheless on both sides are strong.
"The truth is that in the Dominican Republic, I would say the national pastime is not baseball. The national sport is politics," said Mauricio De Vegoechea, a political analyst.
The boisterous campaigns stretched from the island to New York, where there is a large population of Dominicans.
Ahead of Sunday's vote, some 200 foreign electoral observers were in the country, and 60,000 police and troops were deployed for security.
"The big difference, obviously, is that one of these candidates was already president and showed us who he was, and the other candidate has certainly been close to the government, but has never held the executive position and is known as a very qualified official," said Javier Cabreja, president of the civic group Citizens' Participation.
Mejia, 71, the former president, has a background in agriculture. He served a previous administration as minister of agriculture and became involved in politics at an early age.
Medina, 60, was elected to four-year terms as a lawmaker in 1986, 1990 and 1994. He also served as president of the country's House of Representatives. He twice served as secretary of state.
There are more than 6 million registered voters in the country.
CNN's Camilo Egana and Maria Santana contributed to this report.