Barack Obama has said that after 15 weeks of war with Iran, the US is now “worse off” than before the conflict started in February.

“We’ve now fought a war, spent billions and billions of dollars, you know, put enormous strain on our military. A lot of people have died. And it feels like we’re back where we were before we started the war, except maybe a little bit worse off,” the former US president told NBC News in an interview that aired on Friday.

Obama, who spoke to the outlet before the opening of the Obama Presidential Center in Chicago today, offered remarks on the memorandum of understanding between the US and Iran signed by Donald Trump in Paris earlier this week.

“I am very happy to see a ceasefire,” Obama said. “And I’m hopeful that it holds.”

Obama has been critical of the rationale for the conflict and questioned the first Trump administration’s decision to tear up the 2015 agreement with Iran that was negotiated by the Obama administration. Known as the Joint Comprehensive Plan of Action, or JCPOA, that deal restricted Iran from obtaining or developing a nuclear weapon in exchange for lifting international economic sanctions.

Obama said that under the JCPOA, “Iran had agreed not to develop nuclear weapons”, but noted that Trump then “pulled out of it, which caused then Iran to develop more nuclear capacity”.

The former president’s remarks come as the White House said that JD Vance had delayed a planned trip to Switzerland to lead a new round of talks with the Islamic republic focusing on the nuclear issue.

Mohammad Bagher Ghalibaf, Iran’s chief negotiator, said on Friday that future talks with the US must respect Tehran’s “red lines”, a likely reference to a ceasefire in Lebanon as part of any agreement.

“As we have demonstrated throughout previous negotiations, we remain steadfast in respecting the established conditions and red lines, and in defending the interests of the Iranian nation,” Ghalibaf was quoted as saying by Iran’s official IRNA news agency.

“If the enemy becomes excessive [in its demands], we have proven that we are ready to retaliate and will not hesitate to deliver a stinging response.”

Trump signed the memorandum during a dinner at the Palace of Versailles on Wednesday night, with Vance trumpeting it on Thursday at the White House.

“The peace plan is already bearing fruit for America, as gas prices fall,” Vance said. “Iran’s nuclear program is destroyed, their conventional military is destroyed and their capacity to threaten their neighbors is still largely gone.”

He asked for “a little bit of faith” in Trump over the agreement and said the president “believes in this deal, he is going to see it to completion, and if the Iranians don’t comply, we still have every single tool and point of leverage that we have today”.

But some energy executives believe that demand for oil to restore strategic reserves depleted during the conflict, which largely halted shipments through the strait of Hormuz, could in fact push global oil prices higher.

Neil Chapman, a senior vice-president at Exxon, said physical oil prices could rise as high as $150 or $160 a barrel if oil stocks hit critical levels.

“You can debate whether that’s going to hit those really low levels in two weeks or three weeks. But once you get to that point, then you’ll see prices shoot up,” he said at a conference in New York, according to the Wall Street Journal.

Obama said in his interview with NBC’s Today that he hoped his new center – or presidential library, as such institutions are known – would be a reminder of what the US was like under his leadership.

“There’s no doubt that we are going through a period right now of disruption, polarization,” the former president said.

He added that, although he understands if people “feel as if our democracy, our civic habits and virtues, our shared understanding of how we treat each other has started to crumble”, it was nevertheless important that “we all play a part in assuring that our elected officials are accountable”.

“And that’s not something that I think we can afford to suggest is behind us.”