Japanese Prime Minister Shinzo Abe left Tokyo on Friday for Estonia, kicking off his official visit to Baltic and Eastern European states of Latvia, Lithuania, Bulgaria, Serbia and Romania.

On his agenda is confirming coordination over imposing pressure on the Democratic People's Republic of Korea, among other issues such as expanding the borders of Japanese diplomacy.

But even US President Donald Trump suggested in an interview with The Wall Street Journal on Thursday that he has developed a positive relationship with the DPRK leader Kim Jong-un, but declined to say whether they have spoken.

In a telephone call on Wednesday, Trump told Republic of Korea's President Moon Jae-in that the United States was open to talks with the DPRK "at the appropriate time, under the right circumstances".

On Tuesday, the two sides on the Korean Peninsula had their first high-level talks in two years, with the DPRK announcing its plan to attend the Pyeongchang Winter Olympics in the ROK, which will open on Feb 9.

On Wednesday, Moon said he is open to a summit meeting with the DPRK's top leader.

At a press conference on Thursday, Japanese Chief Cabinet Secretary Yoshihide Suga said that the Japanese government has yet to decide whether Abe will attend the opening ceremony for the Olympics.

Japan's Jiji Press quoted sources as saying that Abe plans to skip it due to the ROK's demand for Japan's official apology for "comfort women", a euphemism for girls and women who were forcibly recruited to serve as sex slaves for Imperial Japanese soldiers before and during World War II.

It is still too early to predict how far the "comfort women" issue will strain Japan-ROK relations and the trilateral ties of China, Japan and the ROK.

Japanese Foreign Minister Taro Kono may visit Beijing on Jan 27-28 for discussions with his Chinese counterpart Wang Yi on improving ties and scheduling the trilateral summit of China, Japan and the ROK, according to the Kyodo News. Japan is eyeing a meeting of Premier Li Keqiang, Abe and Moon in early April.

The trilateral leaders' meeting was last held in November 2015.