South Korea, the United States and Japan are in talks to hold a trilateral meeting of their top diplomats on the sidelines of a United Nations plenary session scheduled for later this month in New York, official sources said Thursday.

The trilateral meeting, if held, will bring together South Korean Foreign Ministry Yun Byung-se, U.S. Secretary of State John Kerry and Japanese Foreign Minister Fumio Kishida when they gather for the U.N. plenary high-level meetings slated from Sept. 19-26, diplomatic sources said.

Details of the three-way meeting are being discussed between the nations, the insider said.

How to put more pressure on a defiant North Korea may dominate the possible trilateral meeting as it comes amid Pyongyang's unrelenting military provocations. Defying international warnings and U.N. resolutions, North Korea launched three ballistic missiles on Monday, which all landed in waters near Japan.

Two weeks earlier, North Korea fired off a submarine-launched ballistic missile (SLBM) off its east coast, the country's third SLBM test so far this year.

On the backdrop of North Korea's unusually frequent military provocations, South Korea and the U.S.' presidents vowed to increase efforts to push for the international community's thorough implementation of U.N. Security Council Resolution 2270 during their summit Tuesday in Vientiane, Laos.

The resolution is the U.N. council's toughest-ever sanctions imposed on Pyongyang following the reclusive regimes fourth nuclear test in January and a long-range rocket launch the next month.

Additional state-level sanctions are also likely to be discussed when the three top diplomats meet in New York.

The three-way talks would also serve as the latest diplomatic gesture to nudge China to work more closely with others to pressure North Korea to give up its military provocations.

Separately, Foreign Minister Yun will deliver a keynote speech to the U.N. plenary session on Sept. 23. The minister's speech will focus on shedding light on the hazard posed by North Korea's nuclear and missile development, and rallying international support behind the implementation of the resolution.

The next day, North Korean Foreign Minister Ri Yong-ho is scheduled to deliver his keynote speech at the U.N. (Yonhap)