Alencar, who is also Brazil's defence minister, said: "We cannot in any way even question the mission. We cannot retreat in any way.
"We are working so that the command remains with Brazil. I don't have any doubt that the command should remain with Brazil."
The news agency later said the government would propose to the UN that army General Jose Elito Carvalho de Siqueira replace Lieutenant-General Urano Teixeira da Matta Bacellar as commander of the peacekeeping forces in Haiti.
Bacellar was found dead from a bullet wound on Saturday in an apparent suicide in his hotel room in Haiti's capital of Port-au-Prince.
Brazilian officials who travelled to Haiti on Sunday said the cause of death still had to be fully investigated.
Army officials said Bacellar had died of a "firearm accident".
The memorial ceremony in Port
au Prince for Lt-Gen Bacellar
According to the Foreign Ministry's press office, Bacellar's body will arrive in Brazil Tuesday. His funeral is scheduled for Wednesday in Rio de Janeiro.
On Monday, Jean-Marie Guehenno, the UN undersecretary-general for peacekeeping, said: "Brazil has made a very strong commitment to Haiti and we would certainly welcome having another Brazilian general to lead the force."
Brazil's command of UN's peacekeeping forces in Haiti has been a key point in the country's foreign policy, which is heavily focused on giving Brazil a permanent seat on the UN Security Council.
Bacellar commanded a 9000-strong peacekeeping force from more than 40 countries that is meant to help restore democracy, two years after a rebellion overthrew Jean-Bertrand Aristide, the former president of Haiti.