Arizona GOP Sen. John McCain, a Vietnam war prisoner, on Saturday criticized President Trump for failing to mention Vietnam's ongoing human rights violations while visiting Da Nang.

“@POTUS in #Danang & no mention of human rights - Sad,” tweeted McCain, who as a Navy pilot was shot down over Hanoi in 1967 and remained a prisoner of war in Vietnam for roughly the next six years.

Trump this weekend, as part of his 12-day Asia tour, praised the Vietnamese people and their leaders for reform efforts, as the country since the end of the war in the mid-1970s has moved away from communist to a more socialist nation.

“Your people are doing a spectacular job,” Trump said Saturday alongside Vietnam President Tran Dai Quang at a state banquet in Hanoi, the nation’s capital. “I toured Vietnam today. I was through the streets of Hanoi, and it's incredible to see. … I would like to congratulate you, Mr. President, on an outstanding job.”

McCain's tweet is the latest in back-and-forth between the Arizona senator and Trump that appeared to start in earnest when the president challenged the senator's status as a war hero during the campaign.

The nonprofit group Human Rights Watch has Vietnam on its list of roughly 200 countries that it considers failing to provide citizens with sufficient human rights such as free speech and freedom of religious beliefs.

“Vietnam’s human rights record remains dire in all areas,” the group says on its website. “The Communist Party maintains a monopoly on political power and allows no challenge to its leadership. … The police use torture and beatings to extract confessions.”