North Korea appears to be preparing a test-launch of an intermediate-range ballistic missile, South Korea's Yonhap news agency says.
It follows what the United States described as the "fiery, catastrophic" failure of the first attempt.
On April 15, the North failed to launch what was likely a Musudan missile, with a range of more than 3000km, meaning it could, if launched successfully, hit Japan and also theoretically put the US territory of Guam within range.
The Musudan missile, which can be fired from a mobile launcher, is not known to have been successfully flight-tested.
North Korea tested its fourth nuclear bomb on January 6 and launched a long-range rocket on February 7, both in defiance of UN resolutions. The North on Saturday conducted a test of a submarine-launched ballistic missile.
"There are indications that the North may fire a Musudan missile that it launched and failed on Kim Il Sung's birthday on April 15," Yonhap quoted an unnamed government official as saying. Kim Il Sung is the North's founder.
North and South Korea remain technically at war after their 1950-53 conflict ended in a truce, rather than a treaty. The North, whose lone major ally is neighbour China, routinely threatens to destroy South Korea and its major ally, the United States.
The April 15 failure was seen as an embarrassing blow for current leader Kim Jong Un, Kim Il Sung's grandson, who has claimed several advances in weapons technology in recent months and is widely expected to conduct a fifth nuclear test soon.
South Korean Defence Ministry spokesman Moon Sang-gyun declined to confirm the Yonhap report but said the North's military would likely spend some time trying to fix the problem following the failed launch.
Experts see North Korea's Musudan test as part of an effort to develop an intercontinental ballistic missile that can reach the mainland United States.
