After months of a peace offensive, North Korea may be gearing up for another missile launch, U.S. experts said Monday.

They note the return of Pak To-chun, a top North Korean official in charge of missile and nuclear development, to a public scene.

Pak, communist party secretary overseeing the munitions industry, had been unusually absent from major reported events since May. His disappearance raised speculation that he might have been purged or demoted due to possible technical glitches in the nation's missile program.

In early September, however, he reappeared in the North's state media. "If indeed his disappearance was caused by the technical setback in the North's missile program, as some observers speculated last summer, then Pak's comeback may indicate that the technical issue must have been successfully resolved and the North may be ready for another missile launch, perhaps as early as this fall," said Alexandre Mansourov, a U.S. expert who has long followed North Korea issues.

In the spring, North Korea issued near-daily threats to launch a missile attack on the U.S. and South Korea. It was seen preparing for the launch of Musudan intermediate-range ballistic missiles from road-mobile launchers. But it did not go ahead with the launch, for unknown reasons.

Citing satellite imagery, a U.S. research institute also said the North probably tested a long-range rocket engine in late August at a launch site near the border with China.

The indicators include the presence of a probable rocket stage, a crane necessary to mount and remove the rocket engine and propellant tanks on the test stand, instrumentation used to monitor tests as well as changes in the appearance of vegetation in front of the flame trench, Nick Hansen, a satellite photo analyst, said

In a report on 38 North, a blog run by the School of Advanced International Studies at Johns Hopkins University. (Yonhap news)