The U.N. Security Council has begun studying stronger sanctions that could be imposed on North Korea in case the communist nation goes ahead with provocations, South Korea's top diplomat said Tuesday.

Foreign Minister Yun Byung-se made the remark to reporters in New York after three-way talks with U.S. Secretary of State John Kerry and Japanese Foreign Minister Fumio Kishida amid growing concern Pyongyang could conduct a long-range rocket launch or a nuclear test.

"The Security Council has begun working-level studies into measures that would be stronger than before and sure to be painful to North Korea," Yun told reporters. "We have to wait and see when and in what form (the measures) will be taken, but North Korea will be further isolated not only economically, but also diplomatically as well."

Yun did not elaborate, but the remark is believed to be the most specific warning yet against North Korea not to forge ahead with provocations. Pyongyang strongly suggested earlier this month it could conduct a long-range rocket launch or its fourth nuclear test, possibly around the Oct. 10 anniversary of its ruling Workers Party.

North Korea was also a top topic for Tuesday's trilateral session.

"North Korea presents an ongoing security challenge to everybody. We will talk about that here this morning," Kerry said at the start of the talks held on the sidelines of the U.N. General Assembly.

Yun said the "eyes of the world" are set on major challenges in Northeast Asia, "especially the publicized address from North Korea on possible strategic provocations in the coming weeks." He said it is important for the three countries to send a clear message to Pyongyang "so that there will not be any misjudgment and misbehavior."

Seoul's Foreign Ministry said the three ministers issued a strong warning to the North.

"With regard to North Korea suggesting a long-range rocket launch, the three foreign ministers expressed serious concern and strongly urged North Korea to refrain from provocations that threaten peace and stability in the region and the international community," Seoul's Foreign Ministry said in a statement.

"The three ministers also made clear that North Korea would face further significant measures from the international community if it goes ahead with provocations despite repeated calls for restraint from the international community, including China and Russia," it said.

The ministers also urged North Korea to return to meaningful denuclearization negotiations, it said.

Yun told reporters that the three ministers discussed deterring North Korean provocations and shared a common position that the international community will take "swift and stern" action if Pyongyang forges ahead with provocations.

"We have sent clear messages to North Korea through a series of summit meetings, including the U.S.-China summit, that North Korean provocations are unacceptable," Yun told reporters, referring to last week's summit between U.S. President Barack Obama and Chinese President Xi Jinping.

After Friday's summit, Xi issued an unusually strong warning to Pyongyang, saying China opposes any actions that might "cause tension in the Korean Peninsula or violate U.S. Security Council resolutions." Obama also said North Korea won't be accepted as a nuclear weapons state.

Officials say North Korea is more likely to conduct a long-range rocket than a nuclear test. That's a typical pattern of Pyongyang's provocation cycle: Conducting a rocket launch and using international condemnations and sanctions for it as an excuse for a nuclear test.

 North Korea says its rocket launches are aimed at putting satellites into orbit, claiming it has the right to peaceful use of space. But Pyongyang is banned from such launches under U.N. Security Council resolutions as it has been accused of using them as a cover for testing intercontinental ballistic missiles.

Experts say long-range rockets and ICBMs are basically the same with differences only in payloads.

Meanwhile, Yun said that the three ministers also reconfirmed that Japan's exercise of its collective self-defense right should be carried out in a way that is transparent and respects South Korea's sovereignty.

The recent passage of security legislation in Japan has empowered the country's Self-Defense Forces to fight overseas in the name of aiding allies. The move sparked concern that Japanese forces could enter the Korean Peninsula in the name of helping the U.S. in the event of war with North Korea.

Japanese boots on the peninsula are one of the last things South Koreans want to see due to painful memories of Japan's colonial rule of Korea from 1910 to 1945. South Korea has said Japanese forces cannot enter the peninsula unless there is explicit consent from Seoul. (Yonhap)