South Korea's intelligence agency says North Korea may fire a newly developed solid-fuel intercontinental ballistic missile for the first time in March or April.

The National Intelligence Service briefed the parliamentary intelligence committee on Pyongyang's moves in a closed-door meeting on Tuesday.

Lawmakers who attended the meeting said the North is expected to conduct a large-scale military exercise involving nuclear forces in March and April. The drills are likely to include the firing of a new solid-fuel ICBM. Solid fuel enables quicker launches of missiles compared to conventional liquid fuel.

The spy agency reportedly said the North may launch a military reconnaissance satellite in April under the country's leader Kim Jong Un's instruction.

It also said Pyongyang could test-launch an ICBM to fly at a normal trajectory while curbing its flight distance.

North Korea is reacting sharply to planned joint military exercises by the United States and South Korea scheduled to begin next Monday.

The North Korean leader's sister, Kim Yo Jong, released a statement on Tuesday saying Pyongyang is "always on standby to take appropriate, quick and overwhelming action."

The South is on alert for possible provocations by the North in response to the projected joint drills.