Talks between Tokyo and Pyongyang on the abduction of Japanese citizens during the Cold War opened in Beijing on Tuesday, with Tokyo's envoys giving the North Koreans a diplomatic rebuke over missile launches.

Sunday's test launch of two short-range Scud missiles was "extremely regrettable", Junichi Ihara, the head of Japan's delegation, told his North Korean counterpart Song Il-Ho as talks got under way at Pyongyang's embassy in the Chinese capital.

Speaking in front of international journalists -- who are rarely allowed in the embassy -- Ihara stressed the missile launch was "incompatible" with the substance of previous North Korean commitments made to Japan and to agreements at Six-Party nuclear talks.

Ihara called on the nuclear-armed North not to repeat the launches, and to respond to the demands of the international community, but Song defended Pyongyang's actions.

"The rocket launch... was carried out smoothly without having the slightest impact, not only on regional peace and security but on international navigation order and ecological environment," Song said.

The talks were held in a huge meeting room under two giant, imposing pictures of North Korea's founder Kim Il-Sung and his son, Kim Jong-Il, who died in 2011.

The younger man was in turn succeeded by his own son Kim Jong-Un, as the dynasty maintains its grip on the secretive, isolated state.

- Kidnappings highly sensitive in Japan -

The Beijing talks are aimed at checking progress in Pyongyang's promised investigation into the fate of Japanese citizens abducted during the 1970s and 1980s to train North Korean spies.

North Korea made the surprise pledge in May after Japan said it could ease its sanctions if Pyongyang carries out a fresh investigation.

The agreement, following three days of talks in Stockholm, was seen as a major breakthrough in a highly strained relationship, and the most positive engagement between Pyongyang and the outside world in many months.

North Korea admitted in 2002 that it had kidnapped 13 Japanese citizens to train its spies in Japanese language and customs. The subject is highly charged in Japan, where there are suspicions that dozens or perhaps even hundreds more were taken.

The North has promised to use the Beijing meeting to "explain about the organisation, composition and persons in charge" of a committee it has set up to reinvestigate the abductions, Tokyo officials said previously.

Ihara and Song were chief negotiators at the breakthrough Stockholm talks.

"What is truly important is what comes next," Ihara said Tuesday. "It's necessary to firmly and steadily implement this agreement and make it effective."

The North's missile launch came three days after Pyongyang fired what were believed to be three short-range missiles into the sea.

The show of force came ahead of a state visit to Seoul by Chinese President Xi Jinping on Thursday to discuss issues including the North's nuclear weapons programmes.

Japan and North Korea have no diplomatic ties and contact each other through their embassies in Beijing at present.

A Chinese foreign ministry official said Beijing hopes the two can establish diplomatic relations.

Vice foreign minister Liu Zhenmin said the normalisation of ties between Tokyo and Pyongyang would be "better for the stability of Northeast Asia" and said he welcomed the two sides using Beijing "as a platform" for dialogue.

"China has always been encouraging the US and Japan to develop normal relations with the DPRK," Liu added, using an abbreviation of the North's official name.