(CNN) -- North Korea is back to its old ways, it seems. South Korea's military has reported that its reclusive northern neighbor test-fired two medium-range ballistic missiles Wednesday morning from a site north of Pyongyang into the sea off its east coast.
The military posturing came while the South's leader, Park Gyuen-hye, met with Japanese Prime Minister Shinzo Abe and U.S. President Barack Obama on the sidelines of the Nuclear Security Summit in The Hague.
South Korean news agency Yonhap reported the three leaders urged tripartite cooperation in the face of North Korean antagonism.
"I think it's very important for our three nations to display this kind of unity and shared determination," President Obama said following the talks.
Japan has registered a "strong protest" with the North Korean embassy in Beijing, Minister for Foreign Affairs Fumio Kishida told a parliamentary session Wednesday. But he said the launch would not affect Japan-North Korea talks scheduled for March 30.
"It is a very important opportunity to make a strong approach to North Korea," he said. "Japan is not considering the change of the plan as of now."
It is believed that two medium-range Rodong missiles -- one at 2.35 AM (local time) and again a few minutes later -- were launched, eventually splashing down in the Sea of Japan, also known by the Koreas as the East Sea.
Several launches of short-range ballistics have been conducted in recent weeks, including one that came within minutes of potentially hitting a Chinese passenger jet. It does not appear that North Korea issued any warnings ahead of Wednesday's launches.
If confirmed, this latest launch marks the first time since 2009 that the DPRK has fired the Rodong class of missile.
"It is a clear violation of U.N. resolution and we demand an immediate stop to (the) provocation," South Korean Ministry of Defense spokesperson Kim Min Suk-fyi said.
Kim added that there are no signs to suggest further launch plans.
Sending a message
The Ministry of Defense in Seoul believes the launch was a reaction to ongoing U.S.-ROK military drills as well as a "message to the international community," given the timing with regards to the Dutch summit.
"These March 26 launches of medium-range No Dong (also known as Rodong) ballistic missiles represent a troubling and provocative escalation that the United States takes very (seriously)," U.S. State Department Deputy Spokesperson Marie Harf said.
"We are closely coordinating with our allies and partners, including in the U.N. Security Council, to take the appropriate measures in response to this latest provocation and to address the threat to global security posed by the DPRK's nuclear and ballistic missile programs."
There are a number of U.N. resolutions restricting ballistic missile launches, including several specifically requiring North Korea to "suspend all activities related to its ballistic missile program and to re-establish a moratorium on missile launches."
While there has been no official reaction from Beijing, North Korea's recent saber-rattling is not going to help relations with China, one of the Stalinist state's few international allies, said John Delury, Assistant Professor of East Asian Studies at Yonsei University Graduate School of International Studies in Seoul.
"There hasn't been any fundamental policy shift but we've seen high ranking Chinese officials express their annoyance pretty consistently," he told CNN. "I think (President) Xi (Jinping) is getting an impression of Kim Jong Un as someone who keeps stirring the pot in ways that are detrimental and undercut the ways which Beijing wants to move. This is not going to improve relations between North Korea and China."
The bellicose move comes at a time when North Korea finds itself increasingly isolated, blaming the United States for the breakdown of the six-party talks, and, according to South Korea's conservative Chosun newspaper, even urging its military and officials "not to trust" China.
Indeed, tensions involving North Korea and its neighbors are rarely out of the headlines. The North Korean state news agency KNCA Wednesday accused South Korean authorities of "hurting the dignity" of North Korea's "supreme leadership" by dropping propaganda leaflets on five North Korean islands.
CNN's Paula Hancocks in Seoul and Junko Ogura in Tokyo contributed to this report