Photo released by Telam of US President Barack Obama and First Lady Michelle Obama as they arrive in Bariloche, Argentina on March 24, 2016. (AFP)
President Barack Obama paid homage on Thursday to victims of Argentina's former US-backed dictatorship, admitting the United States was "slow to speak out for human rights" in those dark days.
Obama became the first US president to formally acknowledge the victims of the 1976-1983 military regime, which declassified documents have revealed was supported by top US officials.
"There's been controversy about the policies of the United States early in those dark days, and the United States, when it reflects on what happened here, has to examine its own policies as well, and its own past," Obama said.
He spoke at Remembrance Park, a monument in Buenos Aires to the 30,000 people who were killed or went missing under the dictatorship.
"Democracies have to have the courage to acknowledge when we don't live up to the ideals that we stand for; when we've been slow to speak out for human rights. And that was the case here."
Paying tribute to victims' families, Obama reprised a historic phrase from the 1985 trial of Argentina's dictators, that "never again" ("nunca mas") must dictators prevail.
"You are the ones who ensure that the past is remembered and the promise of 'nunca mas' is finally fulfilled."
Coup AnniversaryObama's visit coincided with the 40th anniversary of a right-wing military coup that ushered in the dictatorship.
After the memorial ceremony, Obama with his wife Michelle and their teenage daughters left Buenos Aires, where mass demonstrations were planned in memory of the victims.
Victims' groups had been angered by the choice of the date for Obama's visit, given the US support for the coup at the time.
But they welcomed his promise to declassify further documents to shed more light on the fates of the regime's victims.
The Obamas flew to the Andean resort of Bariloche, where they went for a hike in a national park.
Locals lined the road smiling and waving as Obama's motorcade took the family from Bariloche airport, but at one place a crowd of protesters demonstrated noisily.
Tango DiplomacyObama has tried to present a softer side of US power in Latin America during a trip that took him first to Cuba and then Argentina.
In Havana, he attended a baseball match with Cuba's Communist President Raul Castro and even made an appearance playing dominoes in a television show with Cuban comedians.
In Buenos Aires, he joked about tasting Argentina's national beverage mate and trying to meet football superstar Lionel Messi.
He danced tango at a state dinner in the city on Wednesday.
The troubled history of US involvement in the region reared its head on Thursday's anniversary.
In 2002, Washington declassified 4,000 diplomatic cables that showed US officials encouraged the Argentine junta's purge of leftists.
Obama agreed ahead of his visit to declassify other sensitive military and intelligence records linked to the "dirty war."
They may shed more light on US involvement in secret police operations in other South American states including Chile, Uruguay, Bolivia and Brazil.
US CreditorsOn the first bilateral visit by a US president to Argentina since Bill Clinton's in 1997, Obama hoped to nurture a new regional ally.
He praised Argentine President Mauricio Macri for the economic reforms he has passed since taking office.
Macri won an election in November, ending 12 years of crisis-ridden leftist rule by the late Nestor Kirchner and his wife Cristina, who had combative political relations with Washington.
Obama praised Macri's "constructive approach" in reaching a deal with US creditors to settle debts dating to Argentina's financial crisis in 2002.
He said it had led to the "possibility of a resolution" that could let Argentina back into international financial markets.