Kim Yo-jong, North Korean leader Kim Jong-un's sister, has said her country's military spy satellite will soon enter orbit and promised Pyongyang will increase military surveillance, state media KCNA reported on Thursday.
"We are ready to act whatever it may be in defending its sovereign right and interests," Ms Kim, a powerful government official, told the agency.
Her remarks follow the failure of a North Korean satellite launch on Wednesday.
The launch appeared to have been rushed and the North may need several weeks at least to fix its rocket's problem, a South Korean politician said on Wednesday, quoting the South's intelligence agency.
In a rare admission of failure by North Korea, KCNA reported that a rocket carrying a military reconnaissance satellite known as Malligyong-1 crashed into the sea after an accident.
It also published images of what it said was the new Chollima-1 rocket lifting off with flames and smoke from a coastal launch pad.
The white-and-grey rocket had a bulbous nose, apparently for carrying its satellite payload.
The launch was widely criticised, including by South Korea, Japan and the US.
UN Secretary General Antonio Guterres said any launch by Pyongyang using ballistic missile technology breaches Security Council resolutions, a spokesman said.
Ms Kim said the criticism of Wednesday's test were "self-contradiction", as the US and other countries have already launched "thousands of satellites".
In a separate statement carried by KCNA, North Korea's vice foreign minister Kim Son-gyong criticised US-led military drills in the region, including a multinational anti-proliferation naval drill.
