Japan's foreign minister has told the BBC that he has been telling the two prospective Conservative leaders to avoid a no-deal Brexit.
Taro Kono told the Today programme that he knew Boris Johnson and Jeremy Hunt "very well" and had told them in meetings, "please no no-deal Brexit".
He said trade talks could not take place until the UK leaves the EU.
Japanese firms were "very concerned" about the implications of the UK leaving the EU without a deal, he said.
Speaking to the BBC ahead of the up-coming G20 meeting in Osaka, he said he had urged both Mr Hunt - the current foreign secretary - and his predecessor, Mr Johnson, to give clarity on Brexit.
"Whenever we had a meeting, that was one of the major issues - please... no no-deal Brexit," he said.
"There are over 1,000 Japanese companies operating in the United Kingdom so we are very concerned with this no-deal Brexit. That would have [a] very negative impact on their operations.
"So whoever wins, whoever becomes a new leader for the UK, [I hope] they would consider those foreign companies operating in the United Kingdom and take good care of it".
During the current leadership campaign, Mr Johnson has said he will get the UK out of the EU on 31 October, but he thinks the chances of a no-deal Brexit happening are a "million to one".
Mr Hunt has said he would leave the EU with no deal, but it is not his preferred option.
Mr Kono said Japan did not want to disrupt economic relations with the UK.
"So we've been asking the UK government, let the Japanese companies know what they can expect, and things should happen smoothly without any disruption".
He gave the example of carmakers, worried about the free flow of parts to the UK from the EU if there was a no-deal Brexit.
"Right now they have very smooth operations. Their stock for each part is only for a few hours. But if there is no-deal Brexit, and if they have to go through actual custom inspection physically, those operations may not be able to continue.
"And many companies are worried about [the] implications because they don't know what's going to happen," he said, so they have started to move their operations to other places in Europe.
He also doubted the UK could sign a new trade deal with Japan - or other nations - before leaving the EU.
"I don't think so," said Mr Kono when asked if he thought it was possible, adding there would be "some kind of gap" before a deal could be agreed.
It was possible the UK could join the Trans-Pacific Partnership trade pact, he said. But again, he said negotiations could not take place until the UK had left the EU.
There would be "some kind of gap" before a deal could be ratified.
But he would like to strengthen the relationship between the two countries, he said.
The president of the largest Japanese company in the UK, Fujitsu, also told the BBC that the Brexit-related uncertainty was difficult for his company.
Takahito Tokita, who has worked for Fujitsu in London, said contingency plans had been made.
But when asked if the company - which employs 10,000 people in the UK - could move its offices out of the UK, he said: "No, definitely no."