The North fired two unidentified projectiles off its east coast early Tuesday (Seoul time) and also released a statement denouncing South Korea-US military exercises that began this week.
"We continue to monitor the situation and are consulting closely with our South Korean and Japanese allies," the official told Yonhap News Agency on condition of anonymity.
North Korea conducted two launches, also off its east coast, last week, calling them tests of a new rocket launch system. South Korea said they appeared to involve a new type of short-range ballistic missile, which the North is banned from testing under UN Security Council resolutions.
The first such test in recent weeks occurred on July 25.
North Korea has described the provocations as a warning to South Korea and the US not to go ahead with joint military maneuvers, which the allies kicked off as planned Monday.
Analysts say the tests are also helping the regime improve its weapons capability and strengthen its hand in any future denuclearization talks with Washington.
US President Donald Trump and North Korean leader Kim Jong-un agreed to resume working-level talks when they met at the inter-Korean border on June 30.
But the talks have yet to be scheduled, and Trump has brushed off all three previous launches as "very standard."
He said Friday that while the tests may be in breach of UN Security Council resolutions, they do not violate any agreement between him and Kim.
"He will do the right thing because he is far too smart not to, and he does not want to disappoint his friend, President Trump!" the president tweeted. (Yonhap)