PORT-AU-PRINCE — United Nations peacekeeping forces have stepped up security across a quake-battered Haiti including at political party headquarters in anticipation of Monday’s preliminary announcement about the winners of the country’s presidential and legislative runoff elections.

The presidential runoff pitted former first lady and longtime opposition leader Mirlande Manigat, 70, against Michel Martelly, a well-known singer known as “Sweet Micky.’’ Each is vying to replace President Rene Preval, who is scheduled to end his second presidential term on May 14.

U.N. police and military could be seen patrolling major cities such as Cap-Haitien in the north, Les Cayes in the south and the capital of Port-au-Prince where an armored U.N. vehicle was parked outside of the Provisional Electoral Council headquarters in Petionville and the home of council president, Gaillot Dorsinvil. Fearful that the announcement could trigger violence, residents spent the week stocking up on groceries and some business owners spent Sunday boarding up.

“We are reinforcing our presence in specific areas, including all of the political party headquarters,’’ said Jean-Francois Vezina, spokesman for the U.N. police, which is supporting the Haitian National police.

Elections officials are scheduled to announce the preliminary results Monday after a four-day delay. The final decision, following appeals by losing candidates, is due April. 16.

Colin Granderson, the assistant secretary general for the Caribbean Community who is leading a joint elections observer mission with the Organization of American States, said unlike the chaotic Nov. 28 first round, a lot more tally sheets were scrutinized for fraud and irregularity this time under OAS-issued recommendations.

“The criteria being used are a lot more time consuming despite the fact the number of lawyers at the vote tabulation center have increased from six to 16,’’ he said.

Some 60 percent of 25,000-plus tally sheets in the presidential elections were set aside for scrutiny by lawyers. Of them, 1,715 – between 15 to 18 percent of the vote – were set aside from the final results. On Sunday, lawyers were expected to do one last examination to make sure the work was done properly and whether additional sheets would be removed from or added to the preliminary count.

Monday’s announcement comes as about 150 U.S. servicemen arrive for humanitarian work. They are not here to help stabilize the country in anticipation of trouble, U.S. Embassy spokesman Jon Piechowski said.

“This was well planned out in advance,’’ he said.

Still there are concerns about violence, especially if the winner is deemed to be Manigat and not Martelly. Pras Michel, a Martelly supporter and a Haitian-American rapper formerly of the Grammy-award winning hip hop group The Fugees, was accused of followers on his Twitter account of inciting violence when at 9 p.m. Sunday, he tweeted: Machete + gasoline + matches = the will of the people.

Followers responded by asking why was he preaching terror, while Martelly supporters quickly denounced him saying he doesn’t speak on behalf of the presidential candidate. Michel, who was seen in Haiti Saturday night hanging out at the bar at the upscale Karibe hotel in Petionville, could not be reached for comment.

Last month, a the rapper was quoted in a YouTube video saying “They will burn the country if Martelly is not elected president.” He told The Miami Herald at the time that his comments were taken out of context. Martelly also distanced himself from the comments, telling journalists at a press conference that he condemned any acts of violence.

“If the people voted for Manigat, and she wins than life goes on,” he said. “If they choose a candidate and it goes a different way then they will be upset about it. When I say burn the country, I am saying, the people will be in a rage. The people did not agree.”

For days, rumors had been swirling that machetes had been sold out at local stores. Vezina of the U.N. police told The Herald he could not confirm the rumor. “There are a lot of rumors,” he said.