* Presidential vote brought forward from 2015
* Amnesty says nearly 1,000 killed in two days
* France has voiced frustration with interim leader (Adds quotes from U.S. ambassador, context, details of gunfire)
By Bate Felix
BANGUI, Dec 19 (Reuters) - Authorities in Central African Republic vowed on Thursday to bring forward elections meant to turn the page on a March coup, as a visiting U.S. envoy said those responsible for months of violence must be brought to justice.
The coup by the mostly Muslim Seleka rebel group unleashed a wave of looting, rapes and massacres by its fighters that degenerated into clashes with Christian self-defence militias.
Seleka leader Michel Djotodia, installed as interim president under a deal with regional African states, has been powerless to halt the bloodshed, which has displaced some 600,000 people and stirred fears of a repeat of Rwanda's 1994 genocide.
The deployment of French troops to the former French colony in early December under a U.N. mandate to protect civilians has largely restored calm to the capital Bangui, though there have been isolated revenge lynchings and machete attacks.
Amid frustration in France with Djotodia's government and diplomatic pressure for quick elections, Prime Minister Nicolas Tiangaye said members of a new national electoral authority would be sworn in next week.
"They will be in charge of preparation and organisation of the election, which will take place in 2014," said Tiangaye, a human rights lawyer who, like Djotodia, is barred from running for office.
Djotodia had been due to remain in office until 2015 under the regional deal, but an escalation in violence this month convinced Paris that he was unable to contain the situation.
U.S. ambassador to the United Nations Samantha Power, on a one-day trip to Bangui in which she visited hospitals and churches and met senior government officials, said it was crucial that the interim administration respect the election timetable and then step aside.
"Those responsible for atrocities must be held accountable, that is a very important element of preventing future violence and cycles of violence," Power said after talks with Tiangaye. "Horrific abuses have been carried out in recent days, weeks and months."
The rights group Amnesty International said on Thursday that Seleka had killed nearly 1,000 people in the capital alone over two days in retaliation for an attack by Christian militias on Dec. 5. Sixty bodies of Muslims were also found, it added.
A Reuters reporter said the capital was mostly calm on Thursday, with people in the street selling fresh vegetables shortly before the curfew.
However, gunfire rang out in a northern neighbourhood for about 20 minutes during the evening.
A spokesman said that Chadian troops, part of a 3,000-strong regional African peacekeeping mission, had come under attack from local militias, known as anti-balaka. Six men were seriously injured, he added.
Command of the African mission was transferred on Thursday from the regional Central African bloc to the African Union. Officials say troop numbers will grow to 6,000 by the end of January, adding to France's 1,600.
Central African Republic has a long history of instability and, since it gained independence in 1960, France has intervened there on more occasions than in any other colony.
But Paris - which also has nearly 3,000 troops deployed against an Islamist threat in Mali - is keen to limit its latest intervention, and Central African Republic is seen as a crucial test of Africa's ability to police its own crises.
"We have a duty and obligation to stop this insecurity in Central African Republic," said General Jean-Marie Mokoko, at a ceremony to assume command of the AU mission. "The world is watching us." (Additional reporting by John Irish in Paris and Paul-Marin Ngoupana in Bangui; Writing by Emma Farge; Editing by Daniel Flynn and xxx)