The objects traveled off the peninsula's east coast, and the South Korean military is analyzing the situation, an official from the South Korean Defense Ministry said.
The news came one day after the United Nations Security Council voted to impose a broad array of sanctions against North Korea because of that nation's recent nuclear test and missile launch, both of which defied international sanctions.
The U.N. resolution that brought about the sanctions aims to cripple the economic factors that fuel North Korea's nuclear and ballistic missile programs.
Among other things, it would ban Pyongyang from exporting most of its natural resources and prohibit the supply of aviation fuel to the country, according to Samantha Power, the U.S. ambassador to the United Nations.
Discussions about new sanctions started after North Korea claimed to have successfully tested a hydrogen bomb in January -- its fourth nuclear test.
Then, in February, Pyongyang said it had successfully launched an Earth satellite into orbit via the long-range Kwangmyongsong carrier rocket.
The nuclear test and missile launch outraged the Security Council and worried neighboring nations.
South Korean President Park Geun-hye released a statement Thursday about the new sanctions, thanking the international community for its efforts.
"I sincerely hope that the North will abandon its nuclear development program and embark on a path of change, and I will make further efforts for peace and unification of the Korean Peninsula," the President said.
Japan's chief Cabinet secretary said Thursday his government does not believe there is a threat to Japanese security in relation to the incident.
And China called for calm.
"The current situation on the Korean Peninsula is complicated and sensitive," Chinese Foreign Ministry spokesman Hong Lei said Thursday. "We hope the relevant parties can keep cool heads and not take any actions that will escalate tensions."
Asked by CNN what the latest launchings mean, Russian U.N. Ambassador Vitaly Churkin said "it means they are not drawing the proper conclusions yet."
Japanese U.N. Ambassador Motohide Yoshikawa quietly said, "that's their way of reacting to what we decided." He added that "we will see. They may do something more."
CNN's Richard Roth, Serena Dong, Joshua Berlinger, Holly Yan and Ralph Ellis contributed to this report.
