Donald Trump revealed that he had asked China to delay his forthcoming visit to Beijing while the war with Iran was continuing, as he attempted to strike a united front on Monday with his vice-president JD Vance, who is believed to have been skeptical over attacking Tehran’s regime.

Appearing together with Vance for the first time in two weeks, Trump said he did not think the conflict – which started on 28 February after the US and Israel opened hostilities – would be over this week but predicted victory would be achieved soon.

However, that confident forecast was dampened somewhat when Trump was asked whether he still planned to visit Beijing on 31 March for a summit meeting with the Chinese leader, Xi Jinping.

“We’re speaking to China. I’d love to [go], but because of the war, I want to be here,” Trump said at an Oval Office signing ceremony.

“I have to be here, I feel and so we’ve requested that we delay it a month or so. I’m looking forward to being with them. We have a very good relationship. But … we got a war going on.”

Trump has claimed several times that the war against the theocratic regime – which he has termed an “excursion” – is all but won, trumpeting the devastation the US military has wreaked on Iranian military capacity, the regime’s political leadership and its infrastructure.

But amid criticism that the US and Israel underestimated the vigor of Iran’s response, Trump has called on western allies and China to help reopen the strait of Hormuz, a chokepoint through which 20% of the world’s oil exports flow and which Tehran is now effectively blocking – causing oil prices to soar.

Trump renewed his previous criticisms of countries who have voiced reluctance to send ships into the zone – singling out Britain, which he called “the Rolls-Royce of allies”, and Keir Starmer, the prime minister.

“I say it would be really helpful if you’d send over a couple of ships, and if you have some minesweepers, which they do, it would be very helpful,” Trump said.

“And the prime minister is a nice man. I think he’s a very nice guy. He says, well, I’d like to ask my team. I said, you’re the prime minister, you can make a decision. So it’s very disappointing.”

In addition to closing off and mining the strait – a measure Iran has repeatedly threatened over many years in the event it came under attack – the Iranian military response has included missile attacks on Arab gulf states, including the United Arab Emirates (UAE), Qatar, Kuwait and Bahrain, all of which host US military bases.

Trump hedged when asked if he was surprised that no one had briefed him that these countries might be targeted in the event of a military onslaught against Iran.

“No. Nobody thought they were going to hit,” he said, referring to some of the countries as “Iran’s bankers”.

“They were … I wouldn’t say friendly countries. They were, like, neutral, they were … they lived with them for years here.

“I heard they were sending missiles to UAE. I said, that’s strange. UAE is like the banker for Iran. There was no experts that would say that was going to happen. It’s not a question of, like, gee, should you have known? And if we did know – big deal. We have to do what we have to do.”

Vance – who was present to mark the signing of an initiative he is to lead investigating supposed fraud in Minnesota – accused a journalist of “trying to drive a wedge” between him and Trump after he was asked if he had rethought his previously proclaimed opposition to US military adventures.

The difference between the current campaign and military engagements in Iraq and Afghanistan “is that we have a smart president”, said Vance, who served in the US Marine Corps in Iraq.

“In wars in the past, we’ve had dumb presidents, and I trust President Trump to get the job done, to do a good job for the American people, and to make sure that the mistakes [of] the past aren’t repeated.”

Reports have suggested that Vance is highly doubtful about the Iran war, having previously voiced opposition to the prospect of embarking on military action against the country.

Trump last week admitted that Vance was “philosophically … less enthusiastic” about the war.

On Monday, as Vance stood behind him, Trump said: “JD Has been great … [he] understands better than most. If you give Iran a nuclear weapon, at least a very substantial part of the world would be blown up, and it’ll be used almost immediately.”