PORT-AU-PRINCE, Haiti (AP) -- Haitian presidential and legislative elections, which have been twice postponed, will take place on December 27 with a runoff on January 31, Haiti's prime minister said.

Haiti's constitution requires the new government to take control on February 7. But it's a complex task because of the country's poor infrastructure and because gang violence has made it difficult to register voters in some parts of the country.

Interim Prime Minister Gerard Latortue in a telephone interview said "The decision is firm and final."

The vote for president and 129 legislative seats was originally scheduled for mid- October.

Meanwhile, heavy gunfire from gang members has forced U.N. troops to abandon a house they were using as an observation point in one of the most volatile sections of the capital, a spokesman for the international peacekeeping force said.

Peacekeeping troops planned a counterattack and hoped to establish round-the-clock patrols in the Cite Soleil slum as part of a broader effort to reduce violence in Port-au-Prince ahead of December elections, said U.N. military spokesman Col. El Ouafi Boulbars.