After U.S. President Donald Trump met with North Korean leader Kim Jong-un at the demilitarized zone on Sunday and agreed to restart nuclear talks, Sen. Bernie Sanders warned against mere photo-ops and said serious diplomatic negotiations are needed to secure lasting peace in the region.

"What's going to happen tomorrow and the next day? We need to move forward diplomatically, not just do photo opportunities."

—Sen. Bernie Sanders

"I have no problem with [Trump] sitting down with Kim Jong-un in North Korea or anyplace else. But I don't want it simply to be a photo opportunity. The whole world's media was attracted there," Sanders said Sunday in an interview on ABC's "This Week," referring to the moment when Trump became the first sitting U.S. president set foot in North Korea.

"What's going to happen tomorrow and the next day?" Sanders asked. "He has weakened the State Department.... We need to move forward diplomatically, not just do photo opportunities."

Sanders—a 2020 Democratic presidential candidate—went on to note that Trump has not committed to diplomatic solutions to other conflicts, such as the U.S.-backed Saudi-led assault on Yemen and growing military tensions with Iran, which were sparked by the president's violation of the Iran nuclear accord last year.

"Right now, while he is meeting with Kim Jong-un, he is still provocative in terms of almost moving toward a war with Iran," Sanders said. "He vetoed legislation that I supported and that we won in the Senate and won in the House which would get the United States out of the horrific war in Yemen, which is led by the brutal dictator Mohammed bin Salman of Saudi Arabia."

"So I don't have a problem with him sitting down and negotiating with our adversaries," Sanders said. "I just don't want it do be a photo opportunity. We need real diplomacy."

Watch:

Sen. Bernie Sanders says he has "no problem" with Pres. Trump meeting with Kim Jong Un, adding: "I don't want it simply to be a photo opportunity... we need to move forward diplomatically, not just do photo opportunities." https://t.co/LmRneR8c4z pic.twitter.com/BG31BBbjHv — This Week (@ThisWeekABC) June 30, 2019

Talks between the U.S. and North Korea are set to resume just months after Trump and Kim's failed summit in Vietnam in February.

As the New York Times reported at the time, the Trump administration took a hardline position by demanding that North Korea give up its entire nuclear weapons program before receiving any concessions or relief from U.S. sanctions, ultimately resulting in the collapse of the summit.