The foreign secretary, Jeremy Hunt, has announced a commitment to a new values-based foreign policy, but tempered his vision by warning that unintended consequences – including even a regional Middle Eastern war – could result if the UK broke with Saudi Arabia over the murder of Jamal Khashoggi.

In a keynote speech and a lengthy evidence session at the foreign affairs select committee on Tuesday, Hunt sought to project a new role for a post-Brexit Britain as an advocate of a reformed multilateral order.

He said UK values, including respect for individual and political rights, media freedom and the separation of powers, would be central.

Hunt promised to host a major conference in London next year on media freedom saying that “access to fair and accurate information is the lifeblood of democracy”.

He also warned that it was no longer possible to believe that there would be an “apparently inevitable progress of democracy” around the world.

But his high-level vision immediately came up against his frank reluctance to break with Saudi Arabia over the murder of the Washington Post columnist Khashoggi. Hunt said he did not intend to end arms exports to Saudi Arabia, or to press the Saudis to adopt a more consensual form of government, saying to do so would probably be counter-productive.

He said: “There is a very challenging situation in the Middle East, there is a proxy war between Saudi Arabia and Iran in Yemen, this has the potential to escalate into a much bigger and more dangerous conflict.”

Hunt warned that there was still a risk that Iran could obtain nuclear weapons. “In that context – and looking at other interventions that we have made in that region in the last 20 years – we just have to be very careful about any action we take that there aren’t unintended consequences.”

Hunt said Khashoggi’s death was “nothing short of totally and terribly shocking”, adding it seemed “increasingly likely” that the press accounts of Khashoggi’s brutal death were true. He was not directly asked if he agreed with Turkey that such a brutal murder could only have been carried out without the express endorsement of the Saudi crown prince Mohammed bin Salman.

Promising to be a strategic foreign secretary, he said Britain was facing three great challenges regardless of Brexit: the rise of China, a recession in democracy and the threat to the post-war rules-based international order, including commitments to free trade, and abhorrence of chemical weapons.

“The apparently inevitable progress of democracy since the fall of the Berlin Wall is no more,” he said.

With outdated post-war institutions close to collapse, he said the solution lay in the reform of the bureaucratic structures set up in a different era largely by the US and the west.

He said: “This means delivering UN reform, as advocated by UN secretary general [António] Guterres. It means fairer burden-sharing in Nato, which continues to be the bedrock of European security. It means WTO reform, so we succeed in warding off the dangerous temptations of protectionism. It means reforming the World Bank, so its governance reflects the changing balance of the global economy.”

He added: “It means reforming the structures of the Commonwealth, so there is proper accountability for the secretariat and a more effective decision-making process.”

He also defended the US president, saying that Donald Trump was “not trying to tear down the international order, but wanted to fight for it in a more robust way than his predecessors”.

Hunt disclosed he would be making significant requests for extra resources in the next spending review and portrayed the Foreign Office as the conductor of the UK’s orchestra of foreign-facing departments.

He hinted he would like to realign the relationship with the Department for International Development, saying he was not sure the UK received the credit it deserved.