South Korea's defence minister said that some countries were "ignoring North Korea's unlawful behaviour", which he said threatens to weaken UN sanctions against its missile and nuclear programmes.
China and Russia on Friday ignored a US call for the UN Security Council to condemn North Korea for a recent attempt to launch a satellite and instead blamed the United States for increasing tension on the Korean peninsula.
"This creates holes in sanctions against North Korea passed at the UN Security Council," Defence Minister Lee Jong-sup said in a speech at the Shangri-La Dialogue in Singapore, Asia's top security summit.
On Wednesday, North Korea launched its first spy satellite into space, although it ended in failure, with the booster and payload plunging into the sea. It has vowed to conduct another satellite launch soon.
"Choosing inactivity to North Korea's unlawful behaviour will worsen the security of not only the Korean peninsula, in the Pacific region but also the entire world," Lee said.
The South Korean minister reiterated that coordination with the United States and Japan to deter North Korea was important.
The three countries have agreed to begin sharing North Korean missile warning data in real-time "within this year", South Korea's defence ministry said in a statement after a meeting between the South Korean, US and Japanese defence chiefs.
That is part of a pact agreed in November to speed up information-sharing.
The defence ministers "strongly condemned North Korea's recent long-range ballistic missile launch, under the guise of a so-called satellite", the statement said.
North Korea argues it has a sovereign right to space development.