Diplomats from Japan and North Korea appear to have made little progress during two days of talks.
The kidnapping issue dominated the talks
Both sides gave few concessions on long-standing points of tension, such as the North's abduction of Japanese nationals in the 1970s, officials said.
The talks, held in Beijing, were aimed at normalising relations.
The two sides have not held substantive talks since December 2004, when the Japanese accused North Korea of lying over the abduction issue.
Pyongyang admitted in 2002 that it had kidnapped 13 Japanese to help train its spies.
Five have since returned home, and the North says the rest have died. But Japan believes they and others could still be alive in the North.
Japanese Foreign Minister Taro Aso said on Friday that little progress was being made on resolving this issue.
Snatched in the '70s and '80s
Used as cultural trainers for N Korean spies
Five allowed home in 2002
Five children now freed from N Korea
Eight said to be dead, others missing
"The [North Korean] position is that the issue has been solved, and I have not heard that the atmosphere has suddenly become one in which they show their willingness to solve it in a serious and forward-looking manner," he told Kyodo news agency from Tokyo.
Mr Song admitted on Thursday that his side had not offered up any new solutions to the kidnapping issue, but added that the topic would be discussed again on Friday.
"It is not a matter that can be settled through contact for one or two hours," Japan's Jiji news agency quoted him as saying.
The North has also come to the talks to ask something from the Japanese. It is thought to want to raise the issue of reparations for Japan's often brutal colonial rule of the Korean peninsula from 1910 to 1945.
Japan gave South Korea $500m when the two countries normalised ties in 1965.
Asked whether the two nations planned to set up a working group for each key issue, Mr Song told reporters: "We have not reached there yet."
Japan has offered to normalise relations with North Korea and provide economic aid if it is given the information about the kidnappings.
It has also threatened sanctions if the issue is not resolved.
But cutting all ties could provoke the secretive North, at a time when the international community is trying to coax it towards a deal on giving up its nuclear programme.
A fifth round of multi-party nuclear talks are due to resume in Beijing next Wednesday, China has announced.
The North warned this week that the US was threatening the talks' success by imposing sanctions against North Korean companies.