Washington's top diplomat visited the remains of a Vietnam War era prison on Saturday where American POWs were held, including veteran Republican senator John McCain.
US Secretary of State Rex Tillerson, who is accompanying president Donald Trump on a tour of Asia, stopped by the notorious Hoa Lo prison -- dubbed the "Hanoi Hilton" by imprisoned GIs during the war -- shortly after arriving in the Vietnamese capital.
Much of the building was demolished in the 1990s but a gatehouse remains alongside a museum that is a popular stop-off for tourists in Hanoi.
McCain, a former airforce pilot, was shot down over Hanoi in 1967 and spent more than five years held captive by the North Vietnamese, enduring often brutal conditions, torture and interrogations.
A famous photograph shows an injured McCain being hauled from a Hanoi lake he parachuted into after ejecting from his stricken aircraft.
State Department staffers told reporters that Tillerson had specifically requested to see the prison museum and the lake during his time in Hanoi.
During his visit Tillerson looked at a copy of the photograph, remarking that McCain had the same photo on his office desk.
He also paid a visit to the lake from which the captured pilot was pulled.
McCain has been a rare outspoken critic of Trump from within the Republican party, something that has infuriated the president.
During his election campaign, Trump -- who dodged the draft five times to avoid being sent to Vietnam -- mocked the veteran Republican senator for getting captured.
"He's not a war hero," Trump said. "I like people that weren't captured, ok?"
Tillerson, a former CEO of oil giant Exxon, was preceded by Barack Obama's Secretary of State John Kerry, who also fought in Vietnam.
Last year, during a trip to the Southeast Asian country, Kerry visited the exact spot where a boat he commanded was ambushed by Viet Cong fighters, even meeting and embracing one of his former adversaries.