The allegations of cronyism have also sparked calls for Aso to resign, and are hampering Abe's bid to achieve his long-held ambition of changing the pacifist constitution.
Abe denied that either he or his wife Akie had intervened in the sale or were involved in altering documents related to the deal, in which mention of his and his wife's names were removed.
Mr Kono, referring to the reports Mr Kim might be in Beijing, quipped: "So we never know if someone would come to Tokyo".
A key figure in a document-tampering scandal involving Japan's Finance Ministry on Tuesday refused to testify on exactly how the ministry's Financial Bureau had deliberately altered the documents.
The prime minister again stressed that neither he nor his wife were involved in the sale or the approval given to Moritomo Gakuen to open a private elementary school on the land.
Japanese Prime Minister Shinzo Abe is finalizing details for a summit with U.S. President Donald Trump on April 18 to discuss strategy before a proposed meeting between North Korean and U.S. leaders, a ruling party official told Reuters on Wednesday.
The land in Toyonaka, Osaka Prefecture, was sold in June 2016 for less than $1.3 million, but has a market value of more than $7 million. Any link to Abe or his wife or to Aso would add to pressure on the cabinet.
Sagawa's testimony Tuesday was the first time he has been officially summoned to address parliament under oath.
According to a public opinion survey covered by the liberal Asahi newspaper at the weekend, 48 percent of those polled said Abe and his government should quit, compared to 39 percent who said that wasn't necessary. In contrast with his definitive attitude when denying any involvement of the prime minister and his wife in the matter, Sagawa failed to completely dispel suspicion that bureaucrats curried favor with politicians when handling the land sale.
Those who said they supported Abe slid to 32.6 percent, down 11.7 percentage points from a month ago, while those who said they did not rose 13.2 percentage points to 54.9 percent. "If there's any mistake or falsehood, I will take responsibility". He said in February 2017 that he would step down if he or his wife were found to have influenced the deal.