* Cisse conceded to Keita in Mali's second round vote
* Says will not file complaints about the election
* Plans a stronger opposition alternative
By Daniel Flynn and Tiemoko Diallo
BAMAKO, Aug 13 (Reuters) - Soumaila Cisse, loser in Mali's presidential elections, vowed on Tuesday that he would build the country's first proper opposition in years, as Malians applauded his concession to Ibrahim Boubacar Keita which dispelled fears of fresh conflict.
Cisse conceded defeat late on Monday as it became clear that former prime minister Keita had swept Sunday's second round vote. Keita has promised to restore the pride of a nation riven by a military coup and an Islamist revolt last year.
On the streets of the riverside capital Bamako, residents heaped praise on Cisse's gesture, which avoided a potentially lengthy and acrimonious battle in a country already weary of turmoil.
Television showed Cisse going in person with his wife and children to congratulate Keita and his family at their home.
"Soumaila's conduct was truly impeccable," said Aissata Camara, a pharmacy lab technician. "It was very impressive and very democratic as well. It was a relief for all of us."
Despite alleging ballot stuffing and voter intimidation by security forces, Cisse said he would not present any complaints to the Constitution Court, handing Keita a stronger mandate to undertake reform.
Official results are expected on Wednesday.
"I will not do anything to weaken Mali or undermine the unity of our nation," Cisse told a news conference.
"I will build an alternative group. We will make proposals. We will criticise if necessary. We will promote democracy by opposition. That is what our country needs today."
Cisse said that the leaders of smaller political parties who had backed his presidential run would also join him in the opposition.
Years of political opponents being co-opted into the government meant there has been little open criticism of the state for a long time, eroding Malians' faith in their political system.
A military coup in 2012, sparked by government passivity over a Tuareg separatist revolt in the north of the country, led to such chaos that Islamist rebels were able to seize control of the northern two-thirds of Mali.
It took a French offensive with thousands of troops launched in January to oust the rebels, and France has been pushing for these elections as it draws down its presence in the country.
Keita faces a daunting task of rebuilding a broken nation. He must move quickly to overhaul the armed forces, tackle ingrained graft and negotiate peace with the northern Tuareg fighters, who are clamouring for more autonomy from Bamako, without alienating his southern support base.
He will benefit from some $4 billion in foreign aid pledged at a conference in Brussels in May destined for reconstruction of the former French colony.
Keita has said his top priority will be to secure lasting peace for northern Mali, which has been racked by five bloody rebellions since independence from France in 1960.
International and local observers said that the presidential election was credible, despite some minor irregularities.
(Editing by Raissa Kasolowsky)