Actions – interrupting – You may not interrupt an action by another action, unless the second action:
• is a valid response to the first action or one of its sub-actions; or
• explicitly “suspends play” (according to a card text or rule).

For example, you may make valid responses to the encounter of specific dilemmas during a mission attempt, but you may not play interrupts between dilemma encounters. See actions – step 2: responses