President Barack Obama will move to declassify U.S. military and intelligence records related to Argentina's "Dirty War," the White House said Thursday, aiming to bring closure to questions of U.S. involvement in a notorious chapter in Argentina's history.

Obama's visit to Buenos Aires next week coincides with the 40th anniversary of the 1976 military coup that started Argentina's 1976-83 dictatorship. Little is known about the U.S. role leading up to that period, in which thousands of people were forcibly disappeared and babies systematically stolen from political prisoners.

Susan Rice, Obama's national security adviser, said Obama would use his trip to announce a "comprehensive effort" to declassify more documents, at Argentina's request. She said Obama would also visit Remembrance Park in Buenos Aires to honor victims of the dictatorship.

"This anniversary and beyond, we're determined to do our part as Argentina continues to heal and move forward as one nation," Rice said in a speech ahead of Obama's trip.

The announcement was sure to have a big impact in Argentina, where even today what happened during the dictatorship is often a part of the national discourse.

"This is transcendental. We believe it's a huge gesture," Marcos Pena, the Cabinet chief of Argentine President Mauricio Macri, told local channel Todo Noticias. Pena added that it would be welcomed by human rights groups who have questioned Obama's presence on the anniversary.

The U.S. has previously released 4,000 State Department documents related to that period, but those documents tell only part of the story. Notes from a 1976 meeting between Secretary of State Henry Kissinger and Argentina's foreign minister, for example, seemed to show Kissinger urging his new counterpart to clamp down on dissidents they referred to as "terrorists."

"If there are things that have to be done, you should do them quickly," Kissinger said, according to a transcript the U.S. declassified more than a decade ago.

In Argentina, human rights advocates have repeatedly called for the U.S. to divulge the rest of the information it has in hopes of exposing any wrongdoing.

As part of the new declassification effort, the U.S. will search for additional records related to rights abuses committed by the junta, said a senior Obama administration official, who wasn't authorized to discuss the program by name and requested anonymity. That search will for the first time include records from U.S. intelligence agencies, along with the Pentagon, U.S. law enforcement agencies and records housed in presidential libraries, the official said.

Claudio Avruj, Argentina's secretary of human rights, said opening the archives could shed light on Argentine soldiers trained at the School of the Americas and the so-called Plan Condor, a coordinated effort between South American dictatorships to stamp out dissent through assassinations, torture and repression.

"This is also going to help in the search for grandchildren taken during the dictatorship," said Avruj via Twitter.

Gaston Chillier, executive director of the Buenos Aires-based Center for Legal and Social Studies, said, "These documents could help both in judicial cases of human rights abuses in Argentina and in the public debate about the role of the United States during the dictatorship."

In an interview with The Associated Press on Wednesday, Macri sidestepped questions about whether he would ask Obama to declassify documents, a question activists had been raising ahead of Obama's trip. He also dismissed criticism that Obama's visit overlapped with the 40th anniversary of the coup that ushered in one of Latin America's most brutal dictatorships.

Such opponents "need to realize that important world leaders have a very busy schedule," Macri said, adding that Obama has been a staunch defender of human rights and should be welcomed.

Argentina's government estimates that at least 13,000 people were killed or disappeared during the crackdown on leftist dissidents that became known as the "Dirty War." Activists believe the figure was as high as 30,000.

The administrations of former President Cristina Fernandez, and before her, that of late husband Nestor Kirchner, oversaw massive efforts to try alleged perpetrators of crimes. Hundreds of former military officials have been convicted and jailed for their role in abuses during the dictatorship.

The South American nation also spends millions every year in search of missing, along the way developing a sophisticated DNA bank.