The pictures, which were taken in May, are said to show similar preparations to those that took place before the communist nation’s last submarine launched missile test in August last year.
They have been released amid the middle of a war of words between Donald Trump and the country’s supreme leader Kim Jung-un.
Pyongyang has accused the US President of driving the peninsula to the brink of a nuclear war after he warned that his military was ‘locked and loaded’.
The Pentagon has said that the United States and North Korea would proceed as planned with a joint military exercise despite the risk it will further antagonise the situation.
Joseph Bermudez of 38North said the commercial satellite imagery shots suggest North Korea may be developing the ‘sea-based leg of its nuclear forces.’
He added: ‘Since the July report, netting or tarps have been suspended above both the fore and aft decks of the submarine obscuring any activity taking place beneath them.
‘The only other time this was seen was during May-July 2016 and prior to the failed July 9, 2016 Pukguksong-1 test.’