Trump has said he would be “disappointed” if North Korea is confirmed to be rebuilding a rocket launch site.
Satellite images published on Wednesday suggest Pyongyang is restoring a site it had pledged to scrap.
Work to dismantle the Sohae satellite launch site began last year and was seen as a concession by Pyongyang.
Talks between Mr Trump and North Korean leader Kim Jong-un broke down at a summit in Vietnam last week.
North Korea on Thursday attacked ongoing joint military exercises between Seoul and Washington as an “open challenge” to moves towards peace on the Korean peninsula.
The US and South Korea agreed on Sunday to replace two major war games that take place every spring – the Key Resolve and Foal Eagle drills – with a shorter Dong Maeng or Alliance exercise which kicked off this week, AFP reports.
The move was designed to further ease tensions with the North following the detente since early 2018. The new flare-up comes just days after the US and North Korean leaders held their second summit. The talks broke up early with no progress toward Washington’s goal of getting Pyongyang to give up its nuclear weapons.