North Korea fired several short-range projectiles into the sea on Thursday, hours after the United Nations' Security Council voted to impose tough new sanctions on the isolated state.
South Korean Defence Ministry said it was trying to determine if the projectiles, launched at 10am (0100 GMT) from the North's east coast, were short-range missiles or artillery fire.
First comment on the North's recent actions was made by South Korean President Park Geun-hye, repeating her call for the North to change its behaviour and welcoming the move by the Security Council.
"We will cooperate with the world to make the North Korean regime abandon its reckless nuclear development and end tyranny that oppresses freedom and human rights of our brethren in the North," Park said at a Christian prayer meeting on Thursday.
Also on Thursday, South Korea adopted a long-delayed security law to set up an anti-espionage unit that was passed by parliament late on Wednesday, and another law aimed at improving human rights in North Korea.
Last month, Seoul suspended the operation of a jointly run factory project with the North that had been the rivals' last remaining venue for regular interaction.
In its latest barrage of insults against the South's leader, the North's official media made commentary on Wednesday likening Park to an "ugly female bat", fated to "die in the dreary cave, its body hanging down".
North Korea faces harsh new UN sanctions to starve it of money for its nuclear weapons program following a unanimous Security Council vote on Wednesday on a resolution drafted by the United States and Pyongyang's ally China.
The resolution, which dramatically expands existing sanctions, follows North Korea's latest nuclear test on Jan. 6 and a Feb. 7 rocket launch that Washington and its allies said used banned ballistic missile technology. Pyongyang said it was a peaceful satellite launch.
All cargo going to and from North Korea must now be inspected and North Korean trade representatives in Syria, Iran and Vietnam are among 16 individuals added to a UN blacklist, along with 12 North Korean entities.
Previously states only had to inspect such shipments if they had reasonable grounds to believe they contained illicit goods.
There was no immediate reaction from the North Korean UN mission. The official North Korean news agency KCNA said on Monday the proposed sanctions were "a wanton infringement on (North Korea's) sovereignty and grave challenge to it."
UN Secretary-General Ban Ki-moon welcomed the 15-nation council's move, saying in a statement that Pyongyang "must return to full compliance with its international obligations."
North Korea has been under UN sanctions since 2006 because of its four nuclear tests and multiple rocket launches.
The new UN sanctions close a gap in the UN arms embargo on Pyongyang by banning all weapons imports and exports.
The Security Council's list of explicitly banned luxury goods has been expanded to include luxury watches, aquatic recreational vehicles, snowmobiles worth more than $2,000, lead crystal items and recreational sports equipment.
There is also an unprecedented ban on the transfer to North Korea of any item that could directly contribute to the operational capabilities of its armed forces, such as trucks that could be modified for military purposes.
The new UN measures also blacklist 31 ships owned by North Korean shipping firm Ocean Maritime Management Company (OMM).
Added to the UN sanctions list was the National Aerospace Development Agency, or NADA, the body responsible for February's rocket launch.
Newly blacklisted individuals include a senior official in North Korea's long-range missile program, senior officials at NADA, officials for Tanchon Commercial Bank in Syria and Vietnam, and Korea Mining Development Trading Corporation (KOMID) representatives in Iran and Syria.
An earlier draft would have blacklisted 17 individuals but the proposed designation of a KOMID representative in Russia was dropped from the final version of the resolution.