Japanese Prime Minister Shinzo Abe was tightlipped Wednesday about a surprise visit by a senior aide to Pyongyang, refusing to give details on the purpose of the trip.

"As the prime minister, I have no comment on the matter," Abe told a parliamentary committee the day after special adviser Isao Iijima arrived in the reclusive state.

Iijima was greeted at the airport in Pyongyang by Kim Chol-Ho, vice director of the North Korean Foreign Ministry's Asian Affairs Department, according to Japanese media.

Reports on Wednesday were rife with speculation that the North was trying to thaw icy relations with Japan at a time ties with the US and South Korea have gone into deep freeze after nuclear and missile tests.

The United States, along with its two Asian allies, has increased pressure on Pyongyang to drop its nuclear ambitions and to join the international community.

Beijing has also taken a firmer line with its sometimes wayward ally, offering rare public rebukes that analysts said revealed frustration at Kim Jong-Un's administration.

Despite his wolfish tone, Abe has shown a pragmatic side in foreign relations, reaching out to South Korea and China during his first brief stint as prime minister.

At that time he was the chosen political heir to hugely popular Junichiro Koizumi, who visited Pyongyang for talks with then North Korean leader Kim Jong-Il in September 2002 and May 2004.

Envoy Iijima is known to have played a role in organising those trips -- which were accompanied by Abe -- and is seen as having cultivated his own connections in North Korea.

Popular opinion on North Korea in Japan is coloured by the 2002 admission by Pyongyang that its agents kidnapped Japanese nationals in the 1970s and 1980s to train spies in Japanese language and customs.

Some of those snatched were allowed to return to Japan along with children who were born in the North, but Pyongyang said the rest of them had died.

However, many in Japan believe the North is still holding some and Pyongyang's perceived refusal to come clean has derailed efforts to normalise ties.

Japan's Chief Cabinet Secretary Yoshihide Suga, who also declined to discuss Iijima's visit, said Tokyo stood firm on its mission to resolve the kidnapping issue as well as North Korea's military threats.

"Japan's North Korean policies are clear. With dialogue and pressure, we are working toward a comprehensive resolution of various issues, such as abduction, the nuclear issue and missiles," Suga told a regular press briefing.

"Particularly, abduction is the priority subject that we as the government must resolve," he said.